Deck 6: Thermochemistry

Question 1

For a particular process q = -17 kJ and w = 21 kJ.Which of the following statements is false?

A)Heat flows from the system to the surroundings.
B)The system does work on the surroundings.
C)" $\Delta$ E" = +4 kJ
D)The process is exothermic.
E)None of the above is false.

Answer 1

The system does work on the surroundings.

Question 2

Consider a gas in a 1.0 L bulb at STP that is connected via a valve to another bulb that is initially evacuated.Answer the following concerning what occurs when the valve between the two bulbs is opened.

-What is true about the value of $\Delta$ E?

A)It is greater than zero.
B)It is equal to zero.
C)It is less than zero.
D)More information is needed.
E)None of these.

Answer 2

It is equal to zero.

Question 3

For a particular process q = 20 kJ and w = 15 kJ.Which of the following statements is true?

A)Heat flows from the system to the surroundings.
B)The system does work on the surroundings.
C)" $\Delta$ E" = 35 kJ
D)All of the above are true.
E)None of the above are true.

Answer 3

" $\Delta$ E" = 35 kJ

Question 4

What is the kinetic energy of a 1.56-kg object moving at 94.0 km/hr?

A)5.32 $\times$ 10² kJ
B)6.89 $\times$ 10³ kJ
C)5.32 $\times$ 10^-4 kJ
D)1.06 $\times$ 10³ kJ
E)2.04 $\times$ 10¹ kJ

Question 5

When a system performs work on the surroundings,the work is reported with a negative sign.

Question 6

Calculate the work associated with the expansion of a gas from 42.0 L to 79.0 L at a constant pressure of 14.0 atm.

A)518 L·atm
B)-518 L·atm
C)-1.11 $\times$ 10³ L·atm
D)588 L·atm
E)1.11 $\times$ 10³ L·atm

Question 7

According to the first law of thermodynamics,the energy of the universe is constant.Does this mean that $\Delta$ E is always equal to zero?

A)Yes, $\Delta$ E = 0 at all times,which is why q = -w.
B)No, $\Delta$ E does not always equal zero,but this is only due to factors like friction and heat.
C)No, $\Delta$ E does not always equal zero because it refers to the system's internal energy,which is affected by heat and work.
D)No, $\Delta$ E never equals zero because work is always being done on the system or by the system.
E)No, $\Delta$ E never equals zero because energy is always flowing between the system and surroundings.

Question 8

Consider a gas in a 1.0 L bulb at STP that is connected via a valve to another bulb that is initially evacuated.Answer the following concerning what occurs when the valve between the two bulbs is opened.
What is true about the value of w?

A)It is greater than zero.
B)It is equal to zero.
C)It is less than zero.
D)More information is needed.
E)None of these.

Question 9

A fuel-air mixture is placed in a cylinder fitted with a piston.The original volume is 0.310-L.When the mixture is ignited,gases are produced and 935 J of energy is released.To what volume will the gases expand against a constant pressure of 635 mmHg,if all the energy released is converted to work to push the piston?

A)10.7 L
B)8.02 L
C)11.4 L
D)11.0 L
E)1.78 L

Question 10

Consider a gas in a 1.0 L bulb at STP that is connected via a valve to another bulb that is initially evacuated.Answer the following concerning what occurs when the valve between the two bulbs is opened.

-What is true about the value of $\Delta$ H?

A)It is greater than zero.
B)It is equal to zero.
C)It is less than zero.
D)More information is needed.
E)None of these.

Question 11

Consider a gas in a 1.0 L bulb at STP that is connected via a valve to another bulb that is initially evacuated.Answer the following concerning what occurs when the valve between the two bulbs is opened.
What is true about the value of q?

A)It is greater than zero.
B)It is equal to zero.
C)It is less than zero.
D)More information is needed.
E)None of these.

Question 12

Which of the following statements correctly describes the signs of q and w for the following exothermic process at P = 1 atm and T = 370 K?
H₂O(g) $\to$ H₂O(l)

A)q and w are negative.
B)q is positive,w is negative.
C)q is negative,w is positive.
D)q and w are both positive.
E)q and w are both zero.

Question 13

A gas absorbs 0.0 J of heat and then performs 30.7 J of work.The change in internal energy of the gas is

A)61.4 J
B)30.7 J
C)-61.4 J
D)-30.7 J
E)none of these

Question 14

A state function does not depend on the system's past or future.

Question 15

A property that is independent of the pathway is called an intensive property.

Question 16

One mole of an ideal gas is expanded from a volume of 1.00 liter to a volume of 8.93 liters against a constant external pressure of 1.00 atm.How much work (in joules)is performed on the surroundings? Ignore significant figures for this problem.(T = 300 K;1 L·atm = 101.3 J)

A)402 J
B)803 J
C)2.41 $\times$ 10³ J
D)905 J
E)none of these

Question 17

Calculate the work associated with the compression of a gas from 121.0 L to 80.0 L at a constant pressure of 13.1 atm.

A)-537 L atm
B)537 L atm
C)3.13 L atm
D)-3.13 L atm
E)101 L atm

Question 18

Which of the following statements is correct?

A)The internal energy of a system increases when more work is done by the system than heat was flowing into the system.
B)The internal energy of a system decreases when work is done on the system and heat is flowing into the system.
C)The system does work on the surroundings when an ideal gas expands against a constant external pressure.
D)All statements are true.
E)All statements are false.

Question 19

Calculate the work for the expansion of CO₂ from 1.0 to 4.7 liters against a pressure of 1.0 atm at constant temperature.

A)3.7 L·atm
B)4.7 L·atm
C)0 L·atm
D)-3.7 L·atm
E)-4.7 L·atm

Question 20

Which statement is true of a process in which one mole of a gas is expanded from state A to state B?

A)When the gas expands from state A to state B,the surroundings are doing work on the system.
B)The amount of work done in the process must be the same,regardless of the path.
C)It is not possible to have more than one path for a change of state.
D)The final volume of the gas will depend on the path taken.
E)The amount of heat released in the process will depend on the path taken.

Question 21

Exactly 123.7 J will raise the temperature of 10.0 g of a metal from 25.0°C to 60.0°C.What is the specific heat capacity of the metal?

A)2.83 J/g°C
B)0.353 J/g°C
C)24.9 J/g°C
D)29.6 J/g°C
E)none of these

Question 22

The enthalpy of fusion of ice is 6.020 kJ/mol.The heat capacity of liquid water is 75.4 J/mol·°C.What is the smallest number of ice cubes at 0°C,each containing one mole of water,necessary to cool 500 g of liquid water initially at 20°C to 0°C?

A)1
B)7
C)14
D)15
E)126

Question 23

Which one of the following statements is false?

A)The change in internal energy, $\Delta$ E,for a process is equal to the amount of heat absorbed at constant volume,q_v.
B)The change in enthalpy, $\Delta$ H,for a process is equal to the amount of heat absorbed at constant pressure,q_p.
C)A bomb calorimeter measures $\Delta$ H directly.
D)If q_p for a process is negative,the process is exothermic.
E)The freezing of water is an example of an exothermic reaction.

Question 24

Consider the reaction H₂(g)+ O₂(g) $\to$ H₂O(l) $\Delta$ H° = -286 kJ
Which of the following is true?

A)The reaction is exothermic.
B)The reaction is endothermic.
C)The enthalpy of the products is less than that of the reactants.
D)Heat is absorbed by the system.
E)Both A and C are true.

Question 25

Consider the reaction: C₂H₅OH(l)+ 3O₂(g) $\to$ 2CO₂(g)+ 3H₂O(l); $\Delta$ H = -1.37 $\times$ 10³ kJ
Consider the following propositions:
I.The reaction is endothermic
II.The reaction is exothermic.
III.The enthalpy term would be different if the water formed was gaseous.
Which of these propositions is (are)true?

A)I
B)II
C)III
D)I,II
E)II,III

Question 26

A 32.5 g piece of aluminum (which has a molar heat capacity of 24.03 J/°C·mol)is heated to 82.4°C and dropped into a calorimeter containing water (specific heat capacity of water is 4.18 J/g°C)initially at 22.3°C.The final temperature of the water is 24.2°C.Ignoring significant figures,calculate the mass of water in the calorimeter.

A)212 g
B)5.72 kg
C)6.42 g
D)1.68 kg
E)none of these

Question 27

What is the specific heat capacity of a metal if it requires 178.1 J to change the temperature of 15.0 g of the metal from 25.00°C to 32.00°C?

A)0.590 J/g°C
B)11.9 J/g°C
C)25.4 J/g°C
D)1.70 J/g°C
E)283 J/g°C

Question 28

C₂H₅OH(l)+ 3O₂(g) $\to$ 2CO₂(g)+ 3H₂O(l), $\Delta$ H = -1.37 $\times$ 10³ kJ For the combustion of ethyl alcohol as described in the above equation,which of the following is true?
I.The reaction is exothermic.
II.The enthalpy change would be different if gaseous water was produced.
III.The reaction is not an oxidation-reduction one.
IV.The products of the reaction occupy a larger volume than the reactants.

A)I,II
B)I,II,III
C)I,III,IV
D)III,IV
E)only I

Question 29

Which of the following properties is (are)intensive properties?
I.mass
II.temperature
III.volume
IV.concentration
V.energy

A)I,III,and V
B)II only
C)II and IV
D)III and IV
E)I and V

Question 30

You take 295.5 g of a solid at 30.0°C and let it melt in 425 g of water.The water temperature decreases from 85.1°C to 30.0°C.Calculate the heat of fusion of this solid.

A)160 J/g
B)166 J/g
C)331 J/g
D)721 J/g
E)cannot solve without the heat capacity of the solid

Question 31

Two metals of equal mass with different heat capacities are subjected to the same amount of heat.Which undergoes the smallest change in temperature?

A)The metal with the higher heat capacity.
B)The metal with the lower heat capacity.
C)Both undergo the same change in temperature.
D)You need to know the initial temperatures of the metals.
E)You need to know which metals you have.

Question 32

A 140.0-g sample of water at 25.0°C is mixed with 111.7 g of a certain metal at 100.0°C.After thermal equilibrium is established,the (final)temperature of the mixture is 29.6°C.What is the specific heat capacity of the metal,assuming it is constant over the temperature range concerned?

A)0.34 J/g°C
B)0.68 J/g°C
C)0.22 J/g°C
D)2.9 J/g°C
E)none of these

Question 33

For the reaction H₂O(l) $\to$ H₂O(g)at 298 K and 1.0 atm, $\Delta$ H is more positive than $\Delta$ E by 2.5 kJ/mol.This quantity of energy can be considered to be

A)the heat flow required to maintain a constant temperature
B)the work done in pushing back the atmosphere
C)the difference in the H-O bond energy in H₂O(l)compared to H₂O(g)
D)the value of $\Delta$ H itself
E)none of these

Question 34

In the lab,you mix two solutions (each originally at the same temperature)and the temperature of the resulting solution decreases.Which of the following is true?

A)The chemical reaction is releasing energy.
B)The energy released is equal to s $\times$ m $\times$$\Delta$ T.
C)The chemical reaction is absorbing energy.
D)The chemical reaction is exothermic.
E)More than one of these.

Question 35

A chunk of lead at 91.6°C was added to 200.0 g of water at 15.5°C.The specific heat of lead is 0.129 J/g°C,and the specific heat of water is 4.18 J/g°C.When the temperature stabilized,the temperature of the mixture was 17.9°C.Assuming no heat was lost to the surroundings,what was the mass of lead added?

A)1.57 kg
B)170 g
C)204 g
D)211 g
E)none of these

Question 36

If 5.0 kJ of energy is added to a 15.5-g sample of water at 10.°C,the water is

A)boiling
B)completely vaporized
C)frozen solid
D)decomposed
E)still a liquid

Question 37

In exothermic reaction,potential energy stored in chemical bonds is being converted to thermal energy via heat.

Question 38

How much heat is required to raise the temperature of a 5.75-g sample of iron (specific heat = 0.450 J/g°C)from 25.0°C to 79.8°C?

A)2.54 J
B)315 J
C)700 J
D)848 J
E)142 J

Question 39

Of energy,work,enthalpy,and heat,how many are state functions?

A)0
B)1
C)2
D)3
E)4

Question 40

A 45.9 g sample of a metal is heated to 95.2°C and then placed in a calorimeter containing 120.0 g of water (c = 4.18 J/g°C)at 21.6°C.The final temperature of the water is 24.5°C.Which metal was used?

A)Aluminum (c = 0.89 J/g°C)
B)Iron (c = 0.45 J/g°C)
C)Copper (c = 0.20 J/g°C)
D)Lead (c = 0.14 J/g°C)
E)none of these

Question 41

On a cold winter day,a steel metal fence post feels colder than a wooden fence post of identical size because:

A)The specific heat capacity of steel is higher than the specific heat capacity of wood.
B)The specific heat capacity of steel is lower than the specific heat capacity of wood.
C)Steel has the ability to resist a temperature change better than wood.
D)The mass of steel is less than wood so it loses heat faster.
E)Two of the above statements are true.

Question 42

Which of the following statements is/are true? I.q (heat)is a state function because $\Delta$ H is a state function and q = $\Delta$ H.
II.When 50.0 g of aluminum at 20.0°C is placed in 50.0 mL of water at 30.0°C,the H₂O will undergo a smaller temperature change than the aluminum.(The density of H₂O = 1.0 g/mL,specific heat capacity of H₂O = 4.18 J/g°C,specific heat capacity of aluminum = 0.89 J/g°C)
III.When a gas is compressed,the work is negative since the surroundings are doing work on the system and energy flows out of the system.
IV.For the reaction (at constant pressure)2N₂(g)+ 5O₂(g) $\to$ 2N₂O₅(g),the change in enthalpy is the same whether the reaction takes place in one step or in a series of steps.

A)I,II,IV
B)II,III
C)II,III,IV
D)II,IV
E)All of the above statements are true.

Question 43

Calculate $\Delta$ H° for the reaction C₄H₄(g)+ 2H₂(g) $\to$ C₄H₈(g),using the following data:
$\Delta$ H°_combustion for C₄H₄(g)= -2341 kJ/mol
$\Delta$ H°_combustion for H₂(g)= -286 kJ/mol
$\Delta$ H°_combustion for C₄H₈(g)= -2755 kJ/mol

A)-128 kJ
B)-158 kJ
C)128 kJ
D)158 kJ
E)none of these

Question 44

What is the specific heat capacity of silver if it requires 86.3 J to raise the temperature of 15 grams of silver by 25°C?

A)4.3 J/g°C
B)0.23 J/g°C
C)0.14 J/g°C
D)0.60 J/g°C
E)none of these

Question 45

What is the enthalpy change when 49.4 mL of 0.430 M sulfuric acid reacts with 23.3 mL of 0.309 M potassium hydroxide? H₂SO₄(aq)+ 2KOH(aq) $\to$ K₂SO₄(aq)+ 2H₂O(l)
$\Delta$ H° = -111.6 kJ/mol

A)-0.402 kJ
B)-3.17 kJ
C)-2.37 kJ
D)-0.803 kJ
E)-112 kJ

Question 46

CH₄(g)+ 4Cl₂(g) $\to$ CCl₄(g)+ 4HCl(g), $\Delta$ H = -434 kJ Based on the above reaction,what energy change occurs when 1.2 moles of methane (CH₄)reacts?

A)5.2 $\times$ 10⁵ J are released.
B)5.2 $\times$ 10⁵ J are absorbed.
C)3.6 $\times$ 10⁵ J are released.
D)3.6 $\times$ 10⁵ J are absorbed.
E)4.4 $\times$ 10⁵ J are released.

Question 47

A 4.4-g sample of Colorado oil shale is burned in a bomb calorimeter,which causes the temperature of the calorimeter to increase by 5.0°C.The calorimeter contains 1.00 kg of water (heat capacity of H₂O = 4.184 J/g°C)and the heat capacity of the empty calorimeter is 0.10 kJ/°C.How much heat is released per gram of oil shale when it is burned?

A)21 kJ/g
B)42 kJ/g
C)0 kJ/g
D)4.9 kJ/g
E)0.21 kJ/g

Question 48

The specific heat capacities of metals are relatively low.

Question 49

The change in enthalpy can always be thought of as equal to energy flow as heat.

Question 50

If a student performs an endothermic reaction in a calorimeter,how does the calculated value of $\Delta$ H differ from the actual value if the heat exchanged with the calorimeter is not taken into account?

A)" $\Delta$ H_calc" would be more negative because the calorimeter always absorbs heat from the reaction.
B)" $\Delta$ H_calc" would be less negative because the calorimeter would absorb heat from the reaction.
C)" $\Delta$ H_calc' would be more positive because the reaction absorbs heat from the calorimeter.
D)" $\Delta$ H_calc" would be less positive because the reaction absorbs heat from the calorimeter.
E)" $\Delta$ H_calc" would equal the actual value because the calorimeter does not absorb heat.

Question 51

Given the equation S(s)+ O₂(g) $\to$ SO₂(g), $\Delta$ H = -296 kJ,which of the following statement(s)is (are)true? I.The reaction is exothermic.
II.When 0.500 mole sulfur is reacted,148 kJ of energy is released.
III.When 32.0 g of sulfur are burned,2.96 $\times$ 10⁵ J of energy is released.

A)All are true.
B)None is true.
C)I and II are true.
D)I and III are true.
E)Only II is true.

Question 52

Consider the following processes:
2A $\to$ (1/2)B + C $\quad$ $\quad$ $\quad$$\quad$$\Delta$ H₁ = 5 kJ/mol
(3/2)B + 4C $\to$ 2A + C + 3D $\quad$$\Delta$ H₂ = -15 kJ/mol
E + 4A $\to$ C $\quad$ $\quad$ $\quad$ $\quad$ $\quad$$\Delta$ H₃ = 10 kJ/mol
Calculate $\Delta$ H for: C $\to$ E + 3D

A)0 kJ/mol
B)10 kJ/mol
C)-10 kJ/mol
D)-20 kJ/mol
E)20 kJ/mol

Question 53

How much heat is liberated at constant pressure when 2.35 g of potassium metal reacts with 5.68 mL of liquid iodine monochloride (d = 3.24 g/mL)? 2K(s)+ ICl(l) $\to$ KCl(s)+ KI(s)
$\Delta$ H° = -740.71 kJ/mol

A)2.22 $\times$ 10³ kJ
B)8.40 $\times$ 10¹ kJ
C)1.28 $\times$ 10² kJ
D)2.23 $\times$ 10¹ kJ
E)7.41 $\times$ 10² kJ

Question 54

The total volume of hydrogen gas needed to fill the Hindenburg was 2.11 $\times$ 10⁸ L at 1.00 atm and 24.7°C.How much energy was evolved when it burned?

A)8.64 $\times$ 10⁶ kJ
B)2.98 $\times$ 10¹⁰ kJ
C)3.02 $\times$ 10⁴ kJ
D)2.47 $\times$ 10⁹ kJ
E)4.94 $\times$ 10⁹ kJ

Question 55

At 25°C,the following heats of reaction are known:

A)-217.5 kJ/mol
B)-130.2 kJ/mol
C)+217.5 kJ/mol
D)-108.7 kJ/mol
E)none of these

Question 56

When 0.236 mol of a weak base (A^-)is reacted with excess HCl,6.91 kJ of energy is released as heat.What is $\Delta$ H for this reaction per mole of A^- consumed?

A)-34.2 kJ
B)-59.4 kJ
C)-29.3 kJ
D)34.2 kJ
E)29.3 kJ

Question 57

The heat of combustion of benzene,C₆H₆,is -41.74 kJ/g.Combustion of 2.82 g of benzene causes a temperature rise of 3.29°C in a certain bomb calorimeter.What is the heat capacity of this bomb calorimeter?

A)387 kJ/°C
B)35.8 kJ/°C
C)0.222 kJ/°C
D)5.96 kJ/°C
E)118 kJ/°C

Question 58

Consider the reaction: When a 21.1-g sample of ethyl alcohol (molar mass = 46.07 g/mol)is burned,how much energy is released as heat?

A)0.458 kJ
B)0.627 kJ
C)6.27 $\times$ 10² kJ
D)2.89 $\times$ 10⁴ kJ
E)2.18 kJ

Question 59

The $\Delta$ H value for the reaction is -90.8 kJ.How much heat is released when 66.9 g Hg is reacted with oxygen?

A)0.333 kJ
B)6.07 $\times$ 10³ kJ
C)30.3 kJ
D)90.8 kJ
E)none of these

Question 60

A bomb calorimeter has a heat capacity of 2.47 kJ/K.When a 0.109-g sample of ethylene (C₂H₄)was burned in this calorimeter,the temperature increased by 2.22 K.Calculate the energy of combustion for one mole of ethylene.

A)-5.29 kJ/mol
B)-50.3 kJ/mol
C)-636 kJ/mol
D)-0.269 kJ/mol
E)-1.41 $\times$ 10³ kJ/mol

Question 61

__________ involves the transfer of energy between two objects due to a temperature difference.

Question 62

Choose the correct equation for the standard enthalpy of formation of CO(g),where $\Delta$ H_f° for CO = -110.5 kJ/mol (gr indicates graphite).

A)2C(gr)+ O₂(g) $\to$ 2CO(g), $\Delta$ H° = -110.5 kJ
B)C(gr)+ O(g) $\to$ CO(g), $\Delta$ H° = -110.5 kJ
C)C(gr)+ O₂(g) $\to$ CO(g), $\Delta$ H° = -110.5 kJ
D)C(gr)+ CO₂(g) $\to$ 2CO(g), $\Delta$ H° = -110.5 kJ
E)CO(g) $\to$ C(gr)+ O(g), $\Delta$ H° = -110.5 kJ

Question 63

Which of the following is both a greenhouse gas and a fuel?

A)carbon dioxide
B)coal
C)freon
D)methane
E)nitrogen

Question 64

Consider the reaction:
N₂(g)+ 3H₂(g) $\to$ 2NH₃(g)
Assuming this reaction takes place in an elastic balloon with an atmospheric pressure of 1.0 atm,and that you have a stoichiometric mixture of nitrogen and hydrogen,draw a microscopic diagram before and after the reaction occurs.See the example below to assist you.
ABC₂(g) $\to$ AB(g)+ C₂(g)(could be drawn as)
In addition,explain whether w (the work done)is positive,negative,or zero.

Question 65

Given: Cu₂O(s)+ O₂(g) $\times$ 2CuO(s) $\quad$$\Delta$ H° = -144 kJ
Cu₂O(s) $\times$ Cu(s)+ CuO(s) $\quad$ $\quad$ $\quad$ $\quad$$\Delta$ H° = +11 kJ
Calculate the standard enthalpy of formation of CuO(s).

A)-166 kJ
B)-299 kJ
C)+299 kJ
D)+155 kJ
E)-155 kJ

Question 66

This fossil fuel was formed from the remains of plants that were buried and exposed to high pressure and heat over time.

A)coal
B)natural gas
C)diesel fuel
D)propane
E)gasoline

Question 67

Consider the reaction: 2ClF₃(g)+ 2NH₃(g) $\to$ N₂(g)+ 6HF(g)+ Cl₂(g)
When calculating the $\Delta$ H°_rxn,why is the $\Delta$ H_f° for N₂ not important?

A)Because nitrogen is in its standard elemental state and no energy is needed for this product to exist.
B)Because any element or compound in the gaseous state requires a negligible amount of energy to exist.
C)Because the products are not included when calculating $\Delta$ H°_rxn.
D)Because nitrogen is in its elemental state and does not contribute to the reaction itself.
E)Two of the above statements explain why N₂ is not important when calculating $\Delta$ H°_rxn.

Question 68

The __________ of a system is the sum of the kinetic and potential energies of all the particles in the system.

Question 69

The heat combustion of acetylene,C₂H₂(g),at 25°C is -1299 kJ/mol.At this temperature, $\Delta$ H_f° values for CO₂(g)and H₂O(l)are -393 and -286 kJ/mol,respectively.Calculate $\Delta$ H_f° for acetylene.

A)2376 kJ/mol
B)625 kJ/mol
C)227 kJ/mol
D)-625 kJ/mol
E)-227 kJ/mol

Question 70

The coal with the highest energy available per unit burned is

A)Lignite.
B)Subbituminous.
C)Bituminous.
D)Anthracite.
E)They are equal in energy value.

Question 71

Using the following thermochemical data,calculate $\Delta$ H_f° of Tm₂O₃(s). 2TmCl₃(s)+ 3H₂O(l) $\to$ Tm₂O₃(s)+ 6HCl(g) $\quad$$\Delta$ H° = 388.1 kJ/mol
2Tm(s)+ 3Cl₂(g) $\to$ 2TmCl₃(s) $\quad$ $\quad$ $\quad$ $\quad$ $\quad$$\Delta$ H° = -1973.2 kJ/mol
4HCl(g)+ O₂(g) $\to$ 2Cl₂(g)+ 2H₂O(l) $\quad$ $\quad$ $\quad$$\Delta$ H° = -202.4 kJ/mol

A)-1888.7 kJ/mol
B)-1787.5 kJ/mol
C)2563.7 kJ/mol
D)-2158.9 kJ/mol
E)1382.7 kJ/mol

Question 72

All of the following statements about the greenhouse effect are true except:

A)It occurs only on earth.
B)The molecules H₂O and CO₂ play an important role in retaining the atmosphere's heat.
C)Low humidity allows efficient radiation of heat back into space.
D)The carbon dioxide content of the atmosphere is quite stable.
E)A and D

Question 73

The heat of formation of Fe₂O₃(s)is -826.0 kJ/mol.Calculate the heat of the reaction when a 53.99-g sample of iron is reacted.

A)-199.6 kJ
B)-399.2 kJ
C)-798.5 kJ
D)-1597 kJ
E)-2.230 $\times$ 10⁴ kJ

Question 74

Using the following thermochemical data:
2Cr(s)+ 6HF(g) $\to$ 0 2CrF₃(s)+ 3H₂(g) $\quad$$\Delta$ H° = -691.4 kJ/mol
2Cr(s)+ 6HCl(g) $\to$ 2CrCl₃(s)+ 3H₂(g) $\quad$$\Delta$ H° = -559.2 kJ/mol
Calculate $\Delta$ H° for the following reaction:
CrF₃(s)+ 3HCl(g) $\to$ CrCl₃(s)+ 3HF(g)

A)-1250.6 kJ/mol
B)132.2 kJ/mol
C)66.1 kJ/mol
D)264.4 kJ/mol
E)-625.3 kJ/mol

Question 75

The following statements concerning petroleum are all true except:

A)It is a thick,dark liquid composed mostly of hydrocarbons.
B)It must be separated into fractions (by boiling)in order to be used efficiently.
C)Some of the commercial uses of petroleum fractions include gasoline and kerosene.
D)It was probably formed from the remains of ancient marine organisms.
E)All of its hydrocarbon chains contain the same number of carbon atoms.

Question 76

One of the main advantages of hydrogen as a fuel is that:

A)The only product of hydrogen combustion is water.
B)It exists as a free gas.
C)It can be economically supplied by the world's oceans.
D)Plants can economically produce the hydrogen needed.
E)It contains a large amount of energy per unit volume of hydrogen gas.

Question 77

Using the information below,calculate $\Delta$ H_f° for PbO(s) PbO(s)+ CO(g) $\to$ Pb(s)+ CO₂(g) $\Delta$ H° = -131.4 kJ
$\Delta$ H_f° for CO₂(g)= -393.5 kJ/mol
$\Delta$ H_f° for CO(g)= -110.5 kJ/mol

A)-151.6 kJ/mol
B)-283.0 kJ/mol
C)+283.0 kJ/mol
D)-372.6 kJ/mol
E)+252.1 kJ/mol

Question 78

For the reaction: AgI(s)+ Br₂(g) $\to$ AgBr(s)+ I₂(s), $\Delta$ H° = -54.0 kJ
$\Delta$ H_f° for AgBr(s)= -100.4 kJ/mol
$\Delta$ H_f° for Br₂(g)= +30.9 kJ/mol
The value of $\Delta$ H_f° for AgI(s)is:

A)-123.5 kJ/mol
B)+77.3 kJ/mol
C)+61.8 kJ/mol
D)-77.3 kJ/mol
E)-61.8 kJ/mol

Question 79

Which of the following is not being considered as an energy source for the future?

A)ethanol
B)methanol
C)seed oil
D)shale oil
E)carbon dioxide

Question 80

The combustion of hydrogen gas releases 286 kJ per mol of hydrogen.If 13.0 L of hydrogen at STP was burned to produce electricity,how long would it power a 100-watt (W)light bulb? Assume no energy is lost to the surroundings.(1 W = 1 J/s)

A)27.7 min
B)1.92 days
C)1.66 hr
D)10.3 hr
E)4.61 hr