Deck 3: Energy and Its Conservation

Question 1

Recognize the types of energy of interest to chemists.

Answer 1

NOT ANSWER

Question 2

Understand the first law of thermodynamics and the concepts of heat and work.

Answer 2

Energy is neither created nor destroyed in any process, although it may be transferred from one body to another or transformed from one form into another. The value of a state function does not depend on the path taken or on the rate of the change.

Question 3

Understand the origins of energy changes in chemical reactions.

Answer 3

Breaking bonds is endothermic. Making bonds is exothermic.

Question 4

Apply the principles of calorimetry to determine energy changes in a chemical reaction.

Question 5

Understand and calculate enthalpy and internal energy.

Question 6

Be familiar with our sources of energy.

Question 7

Use the following data for Questions :
Table 3-1; Table 3-2; q = nC?T; w = Force*distance; ?E = q + w

-Al₂O₃ is the raw material for manufacturing aluminum and must be heated considerably before it can be converted to aluminum. Calculate the amount of heat (in kJ) required to heat 200 kg of Al₂O₃ (C = 79.04 J/molK) from 25°C to 1000°C and compare that to the amount of heat required to heat 200 kg of Al metal (C = 24.35 J/molK) from 25°C to 550°C. What is the difference?

A) 9.25 x 10⁵ kJ
B) 9.47 x 10⁴ kJ
C) 7407 kJ
D) 79.04 kJ
E) 1961 kJ

Question 8

Use the following data for Questions :
Table 3-1; Table 3-2; q = nC?T; w = Force*distance; ?E = q + w

-A CRC Handbook of Chemistry and Physics has a mass of about 2.83 kg. How much work must be done against gravity to lift the book from the floor to the shelf 2.0 m off the floor? (Note: the force due to gravity is F_g = m(9.8 m/s²) where m is the mass of the object.)

A) 20 J
B) 40 J
C) 55 J
D) 70 J
E) 85 J

Question 9

Use the following data for Questions :
Table 3-1; Table 3-2; q = nC?T; w = Force*distance; ?E = q + w

-A refrigerator uses a compressor to do work to "remove the heat" from warm things within it. A foam cup containing 150 g of water at 23.0°C is placed in a refrigerator. What is the minimum work the compressor must do to cool the water to 1.5°C?

A) 1.2 kJ
B) 5.6 kJ
C) 13 kJ
D) 18 kJ
E) 56 kJ

Question 10

Use the following data for Questions :
Table 3-1; Table 3-2; q = nC?T; w = Force*distance; ?E = q + w

-A 5.6 g bullet travelling at 650 m/s is stopped upon impact with a pool of water. How much heat is released?

A) 400 J
B) 600 J
C) 1000 J
D) 1200 J
E) 1500 J

Question 11

Use the following data for Questions :
Table 3-1; Table 3-2; q = nC?T; w = Force*distance; ?E = q + w

-How many kJ of energy will be converted to heat when a 1.4 x 10³ kg automobile stops from a speed of 67 km/hr?

A) 240 kJ
B) 265 kJ
C) 290 kJ
D) 315 kJ
E) 400 kJ

Question 12

Nylon is an important component in many products. One step in the production of nylon is the reaction of cyclohexane with oxygen to give cyclohexanone and water, shown below in the balanced reaction in line formula notation. Determine the energy change for this process using bond energies. (See Table 3-2.)

A) ?E = -246 kJ/mol
B) ?E = 246 kJ/mol
C) ?E = -346 kJ/mol
D) ?E = 346 kJ/mol
E) ?E = -305 kJ/mol

Question 13

Estimate ?E for the following reaction using bond energies: (See Table 3-2 in the text)
C₂H_4(g) + Br_{2 (g)} $\rightarrow$ C₂H₄Br_{2 (g)}

A) -275 kJ/mol
B) -90 kJ/mol
C) 90 kJ/mol
D) 275 kJ/mol
E) -360 kJ/mol

Question 14

Based on bond energies, determine the reaction energy per mole of carbon for C₂H_4. (See Table 3-2 in the text )

A) -1280 kJ mol^-1
B) -640 kJ mol^-1
C) 640 kJ mol^-1
D) -1550 kJ mol^-1
E) 775 kJ mol^-1

Question 15

The reaction of ethene, C₂H₄, to form polyethylene is shown below: (See Table 3-2 in the text) Estimate how much energy is released when one mole of ethene forms polyethylene using bond energies.

A) 69 kJ/mol
B) 75 kJ/mol
C) 345 kJ/mol
D) 690 kJ/mol
E) 38 kJ/mol

Question 16

The combustion of an organic compound releases 35.6 kJ of energy and causes the temperature of a constant volume calorimeter to increase by 4.76°C. What is the heat capacity of the calorimeter? (C = 75.291 J/mol.K for H₂O; q = C_cal $\Delta$ T)

A) 3.05 kJ/K
B) 5.67 kJ/K
C) 6.90 kJ/K
D) 7.48 kJ/K
E) 12.3 kJ/K

Question 17

A constant pressure "coffee-cup" calorimeter is used to measure the heat of reaction between 0.10 L of 1.0 M NaOH and 0.10 L of 1.0 M HCl. Both solutions initially are at 24.0°C; after the solutions are mixed, the final temperature is 30.4°C. If the heat capacity of the resulting solution is assumed to be totally due to water (C_p = 75.291 J/mol•K), how much heat was evolved from the reaction per mole of limiting reactant? Assume the density of all solutions is 1.0 g/mL. (C = 75.291 J/mol.K for H₂O; q = C_cal $\Delta$ T)

A) 5.4 kJ/mol
B) 22 kJ/mol
C) 54 kJ/mol
D) 123 kJ/mol
E) 270 kJ/mol

Question 18

At 11:30 pm at a large university on a night during finals week, 7500 students each use an electrical heater to heat 450 g of water from 20°C to 100°C to make a cup of coffee. How many kJ of electrical energy is consumed to make their beverages? Assume 100% efficiency.(C = 75.291 J/mol . K for H₂O; q = C_cal $\Delta$ T)

A) 110 kJ
B) 150 kJ
C) 1.5 x 10⁵ kJ
D) 1.1 x 10⁶ kJ
E) 1.1 x 10⁹ kJ

Question 19

A constant volume calorimeter's temperature increases by 2.34 K when a standard compound is combusted, releasing 2.14 kJ of energy. A 0.5623 g sample of sucrose, C₁₂H₂₂O₁₁, is then combusted in the same calorimeter and a temperature increase of 10.13 K is noted. What is the energy released per mole of sucrose combusted?(C = 75.291 J/mol . K for H₂O; q = C_cal $\Delta$ T)

A) 5623 kJ/mol
B) 5640 kJ/mol
C) 8,434 kJ/mol
D) 10,355 kJ/mol
E) 3168 kJ/mol

Question 20

How much energy is required to heat 450 g of water from 20°C to 100°C?(C = 75.291 J/mol . K for H₂O; q = C_cal $\Delta$ T)

A) 1.5 x 10³ J
B) 3.6 x 10⁴ J
C) 4.5 x 10³ J
D) 1.5 x 10² kJ
E) 3.6 x 10² kJ

Question 21

Lactic acid (line structure below) is an intermediate in the metabolism of glucose.(C = 75.291 J/mol.K for H₂O; q = C_cal $\Delta$ T) When 0.149 g of lactic acid is combusted in a constant volume calorimeter in an excess of oxygen, only CO₂ and water are products and 2.24 kJ of energy is released. If the heat capacity of the calorimeter is 0.827 kJ/K and the initial temperature was 23.44°C, what is the final temperature in °C? (C = 75.291 J/mol.K for H₂O; q = C_cal $\Delta$ T)

A) 2.71°C
B) 26.15°C
C) 25.11°C
D) 27.23°C
E) 28.34°C

Question 22

How much energy in kJ must be absorbed to heat up a volume of ocean water 2 m high by 20 km wide by 30 km deep by 3°C? (The density of sea water is about 1.02 g/mL; it requires about 4.2 J to heat up 1 g of sea water 1 K.) (C = 75.291 J/mol.K for H₂O; q = C_cal $\Delta$ T)

A) 1.2 x 10¹⁰ kJ
B) 5.1 x 10¹² kJ
C) 9.8 x 10¹² kJ
D) 1.5 x 10¹³ kJ
E) 9.8 x 10¹⁵ kJ

Question 23

How much energy must be removed to cool a volume of air 1 km high by 20 km wide x 30 km deep by 5°C? (The density of air is about 1.29 g/L; it requires 1.02 J to heat up 1 g of air 1K.) (C = 75.291 J/mol.K for H₂O; q = C_cal $\Delta$ T)

A) 1.4 x 10¹⁰ kJ
B) 2.6 x 10¹² kJ
C) 4.0 x 10¹² kJ
D) 9.3 x 10¹² kJ
E) 4.0x10⁹ kJ

Question 24

A 1.72 g sample of the saccharide, C₆H₁₂O₆, shown below is combusted in a constant volume calorimeter of heat capacity 8.21 kJ/K. The initial temperature is 22.1°C. The final temperature is 25.4°C. What is the energy released per mole of this sugar upon combustion? (C = 75.291 J/mol.K for H₂O; q = C_cal $\Delta$ T)

A) 2830 kJ/mol
B) 3530 kJ/mol
C) 4565 kJ/mol
D) 5865 kJ/mol
E) 4868 kJ/mol

Question 25

A piece of cauliflower was combusted in a calorimeter with a heat capacity of 5.24 kJ/°C. The temperature increased from 24.35°C to 25.07°C. What was the enthalpy change for the combustion of the cauliflower? (C = 75.291 J/mol.K for H₂O; q = C_cal $\Delta$ T)

A) 3.8 kJ
B) -3.8 kJ
C) 6.5 kJ
D) -6.5 kJ
E) -7.3 kJ

Question 26

What is the work (per mole of water) associated with the chemical process in which hydrogen and oxygen gases combine to form liquid water at 25 ^oC?
( $\Delta$ H_rxn = $\Delta$ H_products - $\Delta$ H_reactants; $\Delta$ H_rxn = Bond broken - Bonds made)

A) +3.7 kJ/mol
B) -3.7 kJ/mol
C) +1.2 kJ/mol
D) -1.2 kJ/mol
E) 7.4 kJ/mol

Question 27

The oxidation of sulphur dioxide to sulphur trioxide is important in the manufacture of sulphuric acid:
2 SO_{2 (g)} + O_{2 (g)} $\rarr$ 2 SO_{3 (g)}
Find the enthalpy change of this reaction given the following:
S _(s) + O_{2 (g)} $\rarr$ SO_{2 (g)}; $\Delta$ H° = -296.83 kJ
2 S _(s) + 3 O_{2 (g)} $\rarr$ 2 SO_{3 (g)}; $\Delta$ H° = -791.44 kJ
( $\Delta$ H_rxn = $\Delta$ H_products - $\Delta$ H_reactants; $\Delta$ H_rxn = Bond broken - Bonds made)

A) -197.78 kJ
B) 197.78 kJ
C) -485.23 kJ
D) 791.22 kJ
E) -1088.27 kJ

Question 28

Determine $\Delta$ H for the following reaction:C₂H_2(g) + 2 H_2(g) $\rarr$ C₂H_6(g); $\Delta$ H =? given the following heats of combustion:
C₂H₂ + 5/2 O₂ $\rarr$ 2 CO₂ + H₂O $\quad$$\Delta$ H = -1300 kJ
H₂ + 1/2 O₂ $\rarr$ H₂O $\quad$$\quad$$\quad$$\quad$$\quad$$\Delta$ H = -286 kJ
C₂H₆ + 7/2 O₂ $\rarr$ 2 CO₂ + 3 H₂O $\quad$$\Delta$ H = -1560 kJ
( $\Delta$ H_rxn = $\Delta$ H_products - $\Delta$ H_reactants; $\Delta$ H_rxn = Bond broken - Bonds made)

A) -154 kJ
B) -256 kJ
C) -312 kJ
D) -648 kJ
E) -3146 kJ

Question 29

The enthalpy and energy changes for a chemical reaction are

A) never the same number.
B) often the same number.
C) are the same when there is no volume change.
D) are the same when all reactants and products are gases.
E) are different when all reactants and products are solids.

Question 30

What is the difference between $\Delta$ H and $\Delta$ E for the reaction at 25^oC of O(g) + N(g) $\rarr$ NO(g)?
( $\Delta$ H_rxn = $\Delta$ H_products - $\Delta$ H_reactants; $\Delta$ H_rxn = Bond broken - Bonds made)

A) 2.5 kJ
B) -2.5 kJ
C) 0.2 kJ
D) -0.2 kJ
E) 0 kJ

Question 31

What is the difference between $\Delta$ H and $\Delta$ E per mole of product, for the reaction at 25 ^oC of O₂(g) + N₂(g) $\rarr$ 2NO(g)?
( $\Delta$ H_rxn = $\Delta$ H_products - $\Delta$ H_reactants; $\Delta$ H_rxn = Bond broken - Bonds made)

A) 5.0 kJ
B) -5.0 kJ
C) 2.5 kJ
D) -2.5 kJ
E) 0 kJ

Question 32

Assume that coal is essentially all carbon and has a density of 1.5 g/mL.1. How much heat is produced if a piece of coal 7cm x 5 cm x 6 cm undergoes complete combustion by the following reaction:
C _(s) + O_{2 (g)} $\rarr$ CO_{2 (g)}; $\Delta$ H = -394 kJ2.
What mass of water could be heated from 25°C to 100°C with this amount of heat?
( $\Delta$ H_rxn = $\Delta$ H_products - $\Delta$ H_reactants; $\Delta$ H_rxn = Bond broken - Bonds made)

A) -1.0 x10⁴ kJ, 3.3 x10⁴g of H₂O
B) +1.0 x10⁴kJ, 33g of H₂O
C) 5.0 x10³kJ, 33 g H₂O
D) -5.0 x10³kJ, 3,300g of H₂O
E) -1.0 x10⁴ kJ, 1.8 x10³g of H₂O

Question 33

Which of the following is the equation corresponding to the formation reaction for nitric acid in the gas phase? ( $\Delta$ Hrxn = $\Delta$ Hproducts - $\Delta$ Hreactants; $\Delta$ Hrxn = Bond broken - Bonds made)

A) H₂ + N₂ + O₂ $\rarr$ HNO₃
B) H (g) + N(g) + 3 O (g) $\rarr$ HNO₃ (g)
C) H (g) + N(g) + O₃ (g) $\rarr$ HNO₃ (g)
D) 1/2 H₂ (g) + 1/2 N₂(g) + 3/2 O₂ (g) $\rarr$ HNO₃ (g)
E) H₂ (g) + N₂(g) + 3 O₂ (g) $\rarr$ 2 HNO₃ (g)

Question 34

Calculate the standard enthalpy change for the combustion of lactic acid, C₃H₆O₃.Given: $\Delta$ H_f° (lactic acid) = -671 kJ/mole; $\Delta$ H_f H₂O = -242.83; CO₂ = -393.5; O₂ = 0 kJ/mol.( $\Delta$ H_rxn = $\Delta$ H_products - $\Delta$ H_reactants; $\Delta$ H_rxn = Bond broken - Bonds made)

A) 345 kJ/mol
B) -656 kJ/mol
C) 1238 kJ/mol
D) -1238 kJ/mol
E) -5346 kJ/mol

Question 35

Calculate the standard enthalpy change for the manufacture of HCl by the following reaction:2 NaCl (s) + H₂SO₄ (l) $\rarr$ 2 HCl (g) + Na₂SO₄ (s)Given: H_f (kJ/mol)= -411.2 (NaCl), -814 (H₂SO₄), -92.3 (HCl), -1387.1 (Na₂SO₄).( $\Delta$ H_rxn = $\Delta$ H_products - $\Delta$ H_reactants; $\Delta$ H_rxn = Bond broken - Bonds made)

A) 64.7 kJ
B) -64.7 kJ
C) -456 kJ
D) 456 kJ
E) -1190 kJ

Question 36

Where does the earth get most of its energy from?

A) aliens
B) sunlight
C) solar winds
D) gravitational friction
E) nuclear power

Question 37

Where do we hope to get most of our energy from in the future?

A) fossil fuels
B) coal
C) biomass
D) hydroelectric dams
E) gasoline

Question 38

In the following processes, identify the type of energy consumed and the type of energy produced. (chemical, electrical, mechanical, gravitational, kinetic, potential, radiant, and/or thermal):
1. A piece of metal is heated and glows bright red.
2. A "lightstick" is bent and begins to glow.
3. A car crashes into a pole and the body metal is warmed.
4. Methane is burned and a hot air balloon rises into the sky.

Question 39

How are the following phenomena consistent with the conservation of energy?
1. A bouncing ball bounces lower each consecutive bounce.
2. A solar panel absorbs light and produces electricity.
3. A car gets worse gas mileage going uphill than on the flats.

Question 40

What is the kinetic energy of a 1000 kg car moving at 30 meters per second? What is the kinetic energy of the same car moving at 60 meters per second? What does this suggest about the distance it takes for the faster car to be stopped by its brakes?

Question 41

What is the kinetic energy of a 114,000 kg jet moving at 750 mph?

Question 42

What is the kinetic energy of a proton moving at 90% of the speed of light? (mass_proton = 1.67262 x10^-27 kg)

Question 43

What is the mass of a jet plane with a kinetic energy of 6.40 x 10⁹ J moving at 750 miles per hour?

Question 44

What is the velocity of a jet plane that has a mass of 114,000 kg and kinetic energy of 9.56 x 10⁸ J?

Question 45

Determine the electrical potential energy between two electrons separated by 100pm.

Question 46

Determine the electrical potential energy between a proton and an electron separated by 100pm.

Question 47

What is the kinetic energy of an electron with a velocity of 2.87 x10⁶ m/s? (mass_electron = 9.109 x10^-31 kg)

Question 48

Is water in a sealed glass tube a closed or isolated system? Give a brief explanation.

Question 49

Is an ice cube with water in a perfect, stoppered thermos an open, closed or isolated system? Give a brief explanation. (Perfect implies that the thermos allows no energy transfer to or from the interior of the thermos.)

Question 50

100 g samples of each silver, aluminum, mercury, copper and iron (molar heat capacities of 25.351, 24.35, 27.983, 24.435 and 25.10 J mol^-1 C^-1, respectively) are subjected to 200 kJ of heat. Which samples sees the largest increase in temperature?

Question 51

Indicate the sign of the thermodynamic quantities in the appropriate box for the given system by placing a mark in the appropriate box:

Question 52

Determine the change in energy of a system when an engine does 25 kJ of work and gives off 30 kJ of heat.

Question 53

Determine the change in energy of a system when an engine does 30 kJ of work while absorbing 40 kJ of heat.

Question 54

Determine the change in energy of a system that absorbs 80 kJ of energy and does 30 kJ of work and releases 25 kJ of heat.

Question 55

The solvent dichloromethane, CH₂Cl₂, is made from the reaction of methane, CH₄, with chlorine gas, Cl₂. The other product of the reaction is hydrogen chloride, HCl. Draw a molecular picture representing the balanced chemical reaction for this process (showing all chemical bonds) and then determine the energy change for the reaction of one mole of methane to give one mole of dichloromethane using bond enthalpies.

Question 56

Using bond energies determine which of CH₄, C₂H₄ and C₂H₆ results in the greatest reaction energy per mole of carbon on combustion to CO₂ and water.

Question 57

Determine the difference in energy between the complete combustion of ethane, C₂H₆ to CO₂ and the incomplete combustion of ethane to CO (base on bond energies, assume bond energy of CO is 1080 kJ mol^-1).

Question 58

Benzene, C₆H₆, is a compound whose Lewis structure has three double bonds. Estimate the energy change upon hydrogenation using bond energies, and calculate the % error, given the true energy change, ?E = -169 kJ/mole.

Question 59

An experiment in a coffee cup calorimeter results in q_rxn = -6 kJ. Is the reaction exothermic or endothermic and will the calorimeter temperature increase or decrease?

Question 60

When 0.891 g of terephthalic acid (line structure below) is combusted in excess oxygen, 17.3 kJ of energy is released. What is the balanced chemical equation for the combustion of terephthalic acid and the energy released per mole upon combustion?

Question 61

A 50 g sample of an unknown metal (listed in the below table) is heated to 100°C and placed in 100 g of water at 22.1°C. The final temperature is 29.0°C. Which of the metals listed is the unknown?

Question 62

A 1200 gram sample of iron is heated to 85 ?C. It is then placed in a bowl that contains 600 grams of water at 18 ?C. What will be the final temperature once equilibrium is established assuming no heat is lost to the surrounding? (C_Fe = 25.10 J/mol.K, C_water = 75.291 J/mol.K)

Question 63

Write the chemical equation of the reaction whose enthalpy change is the standard enthalpy of formation of AlCl_{3 (g)}.

Question 64

A liquid is vaporized at its boiling point. Is this an exothermic process or endothermic?

Question 65

A sample of water is frozen in your refrigerator. Determine if each part of the system is exothermic or endothermic; the water, the refrigerator, the entire system (water and refrigerator).