Question 1

The values of ΔH°_f for the three states of benzene are approximately -22 kcal/mol,-11 kcal/mol,and Which is the value for solid benzene?

Accepted Answer

The answer of The values of ΔH°_f for the three...

Question 2

Heat of formation for CO is -110.5 KJ/mol and the heat of formation for MgO is -602 KJ/mol.Which of the following statements is true?

Accepted Answer

The heat of formation is a measure of the energy released or absorbed when a compound is formed from its constituent elements. A more negative delta Hf indicates a more stable compound, as it requires less energy to form. Since MgO has a more negative heat of formation (-602 kJ/mol) than CO (-110.5 kJ/mol), it means that it is a more stable compound and that the bond in MgO is stronger than the bond in CO. Therefore, the correct answer is B.

Question 3

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

Accepted Answer

The metal with the highest heat capacity undergoes the smallest change in temperature because it can absorb more heat without a significant change in its temperature.

Question 4

Given that ΔH°= -311 kJ for the hydrogenation of acetylene,C₂H₂: H-C C-H(g)+ 2 H₂(g)→ CH₃-CH₃(g) And the following bond dissociation energies,estimate a value for the C-to-C triple bond dissociation energy.

Accepted Answer

The ΔH° for the reaction is the sum of the bond dissociation energies (BDE) of the C-C triple bond and two H-H bonds, minus the BDE of the two C-H bonds formed, plus the ΔH° of formation of the product CH2=CH2. Mathematically,

ΔH°reaction = BDE(C-C) + 2BDE(H-H) - 2BDE(C-H) + ΔH°f(CH2=CH2)

Rearranging the equation and plugging in the given values,

BDE(C-C) = [2BDE(C-H) - ΔH°f(CH2=CH2) - 2×BDE(H-H)]

= [2(413 kJ/mol) - (-84 kJ/mol) - 2(435 kJ/mol)]

= 807 kJ/mol

Therefore, choice C is the best answer.

Question 5

For the reaction 2CH₄ (g)+ 3 Cl₂ (g)→ 2 CHCl₃ (l)+ 3 H₂ (g),ΔH° = -118.6 kJ. ΔH°_f = -134.1 kJ/mol for CHCl₃ (l).Find ΔH°_f for CH₄ (g).

Accepted Answer

The given reaction is: $2CH_4(g) + 3Cl_2(g) \rightarrow 2CHCl_3(l) + 3H_2(g)$, with $\Delta H^\circ = -118.6 \, \text{kJ}$.Given $\Delta H_f^\circ$ for $CHCl_3(l)$ is $-134.1 \, \text{kJ/mol}$.To find $\Delta H_f^\circ$ for $CH_4(g)$, we use the equation for the standard enthalpy change of the reaction ($\Delta H^\circ$) in terms of the standard enthalpies of formation ($\Delta H_f^\circ$) of the reactants and products:$$\Delta H^\circ = \sum \Delta H_f^\circ (\text{products}) - \sum \Delta H_f^\circ (\text{reactants})$$Substituting the given values:$$-118.6 = [2(-134.1) + 3(0)] - [2\Delta H_f^\circ(CH_4) + 3(0)]$$Solving for $\Delta H_f^\circ(CH_4)$:$$-118.6 = -268.2 - 2\Delta H_f^\circ(CH_4)$$$$2\Delta H_f^\circ(CH_4) = -268.2 + 118.6$$$$2\Delta H_f^\circ(CH_4) = -149.6$$$$\Delta H_f^\circ(CH_4) = -74.8 \, \text{kJ/mol}$$

Question 6

Ethyl alcohol is produced by the fermentation of glucose,C₆H₁₂O₆. C₆H₁₂O₆(s)→ 2 C₂H₅OH(l)+ 2 CO₂(g)ΔH° = -69.1 kJ Given that the enthalpy of formation is -277.7 kJ/mol for C₂H₅OH(l)and -393.5 kJ/mol for CO₂(g),find the enthalpy of formation for C₆H₁₂O₆.

Accepted Answer

Using the given thermochemical equation, we can calculate the enthalpy change for the reaction:

ΔH = products - reactants
ΔH = [2(-393.5 kJ/mol) + 2(277.7 kJ/mol)] - (-69.1 kJ/mol)
ΔH = -1273.3 kJ/mol

Since the enthalpy change is for one mole of ethyl alcohol, we can say that the enthalpy of formation for ethyl alcohol is -1273.3 kJ/mol.

To find the enthalpy of formation for glucose, we need to know the enthalpy change for the combustion of glucose. However, this is not given in the problem, so we cannot calculate the enthalpy of formation for glucose.

Therefore, the correct answer is B.

Question 7

Determine the sign of ΔS° for each of the following: I.C₆H₆(s)→ C₆H₆(l) II.2 SO₂(g)+ O₂(g)→ 2 SO₃(g)

Accepted Answer

For I, the transition from solid to liquid (melting) increases disorder, leading to a positive ΔS°. For II, the reaction reduces the number of gas molecules from 3 to 2, decreasing disorder and resulting in a negative ΔS°.

Question 8

Use the given average bond dissociation energies,D,to estimate ΔH for the reaction of methane,CH₄(g),with fluorine according to the equation: CH₄(g)+ 2 F₂(g)→ CF₄(g)+ 2 H₂(g)

Accepted Answer

The answer of Use the given average bond dissociation energies,D,to...

Question 9

The heat of combustion per mole for acetylene,C₂H₂(g),is -1299.5 kJ/mol.Assuming that the combustion products are CO₂(g)and H₂O(l),and given that the enthalpy of formation is -393.5 kJ/mol for CO₂(g)and -285.8 kJ/mol for H₂O(l),find the enthalpy of formation of C₂H₂(g).

Accepted Answer

The answer of The heat of combustion per mole for...

Question 10

Which of the following can be interpreted as a measure of randomness?

Accepted Answer

Entropy is a measure of randomness or disorder within a system. The higher the entropy, the more disordered or random the system is. Therefore, option B can be interpreted as a measure of randomness.

Question 11

Coal gasification can be represented by the equation: 2 C(s)+ 2 H₂O(g)→ CH₄(g)+ CO₂(g)ΔH = ? Use the following information to find ΔH for the reaction above. CO(g)+ H₂(g)→ C(s)+ H₂O(g)ΔH = -131 kJ CO(g)+ H₂O(g)→ CO₂(g)+ H₂(g)ΔH = -41 kJ CO(g)+ 3 H₂(g)→ CH₄(g)+ H₂O(g)ΔH = -206 kJ

Accepted Answer

The correct answer is A because the enthalpy change for the reaction can be calculated using Hess's law:ΔH = ΔH1 + ΔH2 + ΔH3ΔH = (-131 kJ) + (-41 kJ) + (-206 kJ)ΔH = -378 kJHowever, the reaction is written in the reverse direction, so the enthalpy change must be multiplied by -1:ΔH = -(-378 kJ) = 378 kJ

Question 12

Find ΔH° for the reaction C₃H₈(g)+ 5 O₂(g)→ 3 CO₂(g)+ 4 H₂O(l). ΔH° = -2046 kJ for the reaction: C₃H₈(g)+ 5 O₂(g)→ 3 CO₂(g)+ 4 H₂O(g) The heat of vaporization of water is 44.0 kJ/mol.Note that H₂O is a liquid in the first reaction and a gas in the second.

Accepted Answer

The difference in ΔH° between the two reactions is due to the phase change of water from gas to liquid. Since 4 moles of water are involved and the heat of vaporization is 44.0 kJ/mol, the total energy change due to condensation is 4 mol * 44.0 kJ/mol = 176 kJ. To find the ΔH° for the first reaction, subtract this energy from the ΔH° of the second reaction: -2046 kJ - 176 kJ = -2222 kJ.

Question 13

Which of CH₄(g),C₂H₂(g),and CH₃OH(l)provides the most energy per gram upon combustion and which provides the least? CH₄(g)+ 2 O₂(g)→ CO₂(g)+ 2 H₂O(l)ΔH° = -890 kJ 2 C₂H₂(g)+ 5 O₂(g)→ 4 CO₂(g)+ 2 H₂O(l)ΔH° = -2599 kJ 2 CH₃OH(l)+ 3 O₂(g)→ 2 CO₂(g)+ 4 H₂O(l)ΔH° = -1453 kJ

Accepted Answer

The answer of Which of CH₄(g),C₂H₂(g),and CH₃OH(l)provides the most energy...

Question 14

Which thermodynamic function is most related to disorder and probability?

Accepted Answer

Entropy is a measure of the degree of randomness or disorder in a system, as well as the number of possible arrangements of particles. It is directly related to the probability of a particular distribution of energy or matter in a system. Therefore, entropy is the thermodynamic function that is most related to disorder and probability.

Question 15

For the reaction,C₂H₂(g)→ 2 C(g)+ 2 H(g),one would expect

Accepted Answer

The reaction involves breaking bonds in C2H2 to form individual atoms, which requires energy, making ΔH° positive. The reaction also increases disorder as a single molecule breaks into multiple atoms, making ΔS° positive.

Question 16

Given: S (s)+ O₂ (g)→ SO₂ (g)ΔH° = -296.1 kJ 2 SO₃ (g)→ 2 SO₂ (g)+ O₂ (g)ΔH° = 198.2 kJ Find ΔH° for : 2 S(s)+ 3 O₂(g)→ 2 SO₃(g)

Accepted Answer

To solve this problem, we need to use Hess's Law, which states that the enthalpy change for a reaction is the same whether it occurs in one step or is broken down into a series of steps. In other words, we can use the enthalpy changes for the given reactions to find the enthalpy change for the desired reaction. First, we need to manipulate the given reactions to match the desired reaction. We can see that the second reaction has two of the desired product, but we need to get rid of the extra O₂(g). We can do this by reversing the first reaction and doubling it: 2 SO₂ (g) → 2 S (s) + 2 O₂ (g) ΔH° = +296.1 kJ Now we can add these two manipulated reactions together to get the desired reaction: 2 S (s) + 3 O₂ (g) → 2 SO₃ (g) ΔH° = -790.4 kJ Therefore, the answer is A, -790.4 kJ.

Question 17

One method for making ethanol,C₂H₅OH,involves the gas-phase hydration of ethylene,C₂H₄: Estimate ΔH for this reaction from the given average bond dissociation energies,D.

Accepted Answer

The answer of One method for making ethanol,C₂H₅OH,involves the gas-phase...

Question 18

Which equation represents the reaction whose ΔH,represents the standard enthalpy of formation of CHCl₃(l)at 25°C? (i.e. ,for which is ΔH = ΔH°_f of CHCl₃)

Accepted Answer

The equation provided in choice C has all the reactants in their standard states (solid carbon, half mole of hydrogen gas, and 3 halves mole of chlorine gas) and produces one mole of liquid CHCl3, which is its standard state. Since the given ΔH is the standard enthalpy of formation for CHCl3, it can only be measured under standard conditions, which are captured in choice C. The other choices either have non-standard state reactants or products, or do not produce CHCl3 as the sole product.

Question 19

Use the given standard enthalpies of formation to calculate ΔH° for the following reaction 3 Fe₂O₃(s)+ CO(g)→ 2 Fe₃O₄(s)+ CO₂(g).

Accepted Answer

The answer of Use the given standard enthalpies of formation...

Question 20

Calculate the enthalpy of combustion per mole for C₆H₁₂O₆.Assume that the combustion products are CO₂(g)and H₂O(l).

Accepted Answer

The balanced equation for the combustion of C₆H₁₂O₆ is: C₆H₁₂O₆ + 9.5O2(g) → 12CO2(g) + 6H2O(g) + SO2(g) Using the standard enthalpy of formation values for the compounds involved, we can calculate the enthalpy of combustion: ΔHcomb = ∑nΔHf(products) - ∑nΔHf(reactants) ΔHcomb = [12(-393.5) + 6(-241.8) + 1(296.8)] - [1(132) + 11(0) + 1(-296.8) + 16(0) + 1(-110.5) + 12(0) + 6(-285.8)] ΔHcomb = -3379.9 kJ/mol However, this is the enthalpy of combustion per 1 mole of C₆H₁₂O₆, and the question asks for it per mole. We can convert using the molar mass of the compound: M(C₆H₁₂O₆) = 12.01 + (32 + 1 + 112 + 16 + 32 + 16) + 12.01 + 16 + 32 + 16 = 256.02 g/mol 1 mol of C₆H₁₂O₆ = 256.02 g -3379.9 kJ/mol ÷ (256.02 g/mol) = -13.19 kJ/g Multiplying by the molar mass of the products: M(CO₂) = 12.01 + 32 + 16 = 60.01 g/mol M(H₂O) = 1 + 32 + 16 + 16 = 65 g/mol 0.5 mol of CO₂(g) weighs 30.01 g and 0.5 mol of H₂O(l) weighs 32.5 g. Multiplying by the amount of heat released per gram: (-13.19 kJ/g) × (30.01 g + 32.5 g) = -842.46 kJ Rounding to the nearest integer, the enthalpy of combustion per mole is -2816 kJ/mol, which corresponds to choice B.

Quiz 9: Thermochemistry: Chemical Energy

The values of ΔH°_f for the three states of benzene are approximately -22 kcal/mol,-11 kcal/mol,and Which is the value for solid benzene?

Heat of formation for CO is -110.5 KJ/mol and the heat of formation for MgO is -602 KJ/mol.Which of the following statements is true?

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

Given that ΔH°= -311 kJ for the hydrogenation of acetylene,C₂H₂: H-C C-H(g) + 2 H₂(g) → CH₃-CH₃(g) And the following bond dissociation energies,estimate a value for the C-to-C triple bond dissociation energy.

For the reaction 2CH₄ (g) + 3 Cl₂ (g) → 2 CHCl₃ (l) + 3 H₂ (g) ,ΔH° = -118.6 kJ. ΔH°_f = -134.1 kJ/mol for CHCl₃ (l) .Find ΔH°_f for CH₄ (g) .

Ethyl alcohol is produced by the fermentation of glucose,C₆H₁₂O₆. C₆H₁₂O₆(s) → 2 C₂H₅OH(l) + 2 CO₂(g) ΔH° = -69.1 kJ Given that the enthalpy of formation is -277.7 kJ/mol for C₂H₅OH(l) and -393.5 kJ/mol for CO₂(g) ,find the enthalpy of formation for C₆H₁₂O₆.

Determine the sign of ΔS° for each of the following: I.C₆H₆(s) → C₆H₆(l) II.2 SO₂(g) + O₂(g) → 2 SO₃(g)

Use the given average bond dissociation energies,D,to estimate ΔH for the reaction of methane,CH₄(g) ,with fluorine according to the equation: CH₄(g) + 2 F₂(g) → CF₄(g) + 2 H₂(g)

The heat of combustion per mole for acetylene,C₂H₂(g) ,is -1299.5 kJ/mol.Assuming that the combustion products are CO₂(g) and H₂O(l) ,and given that the enthalpy of formation is -393.5 kJ/mol for CO₂(g) and -285.8 kJ/mol for H₂O(l) ,find the enthalpy of formation of C₂H₂(g) .

Which of the following can be interpreted as a measure of randomness?

Find ΔH° for the reaction C₃H₈(g) + 5 O₂(g) → 3 CO₂(g) + 4 H₂O(l) . ΔH° = -2046 kJ for the reaction: C₃H₈(g) + 5 O₂(g) → 3 CO₂(g) + 4 H₂O(g) The heat of vaporization of water is 44.0 kJ/mol.Note that H₂O is a liquid in the first reaction and a gas in the second.

Which thermodynamic function is most related to disorder and probability?

For the reaction,C₂H₂(g) → 2 C(g) + 2 H(g) ,one would expect

Given: S (s) + O₂ (g) → SO₂ (g) ΔH° = -296.1 kJ 2 SO₃ (g) → 2 SO₂ (g) + O₂ (g) ΔH° = 198.2 kJ Find ΔH° for : 2 S(s) + 3 O₂(g) → 2 SO₃(g)

One method for making ethanol,C₂H₅OH,involves the gas-phase hydration of ethylene,C₂H₄: Estimate ΔH for this reaction from the given average bond dissociation energies,D.

Which equation represents the reaction whose ΔH,represents the standard enthalpy of formation of CHCl₃(l) at 25°C? (i.e. ,for which is ΔH = ΔH°_f of CHCl₃)

Use the given standard enthalpies of formation to calculate ΔH° for the following reaction 3 Fe₂O₃(s) + CO(g) → 2 Fe₃O₄(s) + CO₂(g) .

Calculate the enthalpy of combustion per mole for C₆H₁₂O₆.Assume that the combustion products are CO₂(g) and H₂O(l) .

Quiz 9: Thermochemistry: Chemical Energy

The values of ΔH°f for the three states of benzene are approximately -22 kcal/mol,-11 kcal/mol,and Which is the value for solid benzene?

Heat of formation for CO is -110.5 KJ/mol and the heat of formation for MgO is -602 KJ/mol.Which of the following statements is true?

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

Given that ΔH°= -311 kJ for the hydrogenation of acetylene,C2H2: H-C C-H(g) + 2 H2(g) → CH3-CH3(g) And the following bond dissociation energies,estimate a value for the C-to-C triple bond dissociation energy.

For the reaction 2CH4 (g) + 3 Cl2 (g) → 2 CHCl3 (l) + 3 H2 (g) ,ΔH° = -118.6 kJ. ΔH°f = -134.1 kJ/mol for CHCl3 (l) .Find ΔH°f for CH4 (g) .

Ethyl alcohol is produced by the fermentation of glucose,C6H12O6. C6H12O6(s) → 2 C2H5OH(l) + 2 CO2(g) ΔH° = -69.1 kJ Given that the enthalpy of formation is -277.7 kJ/mol for C2H5OH(l) and -393.5 kJ/mol for CO2(g) ,find the enthalpy of formation for C6H12O6.

Determine the sign of ΔS° for each of the following: I.C6H6(s) → C6H6(l) II.2 SO2(g) + O2(g) → 2 SO3(g)

Use the given average bond dissociation energies,D,to estimate ΔH for the reaction of methane,CH4(g) ,with fluorine according to the equation: CH4(g) + 2 F2(g) → CF4(g) + 2 H2(g)

The heat of combustion per mole for acetylene,C2H2(g) ,is -1299.5 kJ/mol.Assuming that the combustion products are CO2(g) and H2O(l) ,and given that the enthalpy of formation is -393.5 kJ/mol for CO2(g) and -285.8 kJ/mol for H2O(l) ,find the enthalpy of formation of C2H2(g) .

Which of the following can be interpreted as a measure of randomness?

Find ΔH° for the reaction C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(l) . ΔH° = -2046 kJ for the reaction: C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(g) The heat of vaporization of water is 44.0 kJ/mol.Note that H2O is a liquid in the first reaction and a gas in the second.

Which of CH4(g) ,C2H2(g) ,and CH3OH(l) provides the most energy per gram upon combustion and which provides the least? CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l) ΔH° = -890 kJ 2 C2H2(g) + 5 O2(g) → 4 CO2(g) + 2 H2O(l) ΔH° = -2599 kJ 2 CH3OH(l) + 3 O2(g) → 2 CO2(g) + 4 H2O(l) ΔH° = -1453 kJ

Which thermodynamic function is most related to disorder and probability?

For the reaction,C2H2(g) → 2 C(g) + 2 H(g) ,one would expect

Given: S (s) + O2 (g) → SO2 (g) ΔH° = -296.1 kJ 2 SO3 (g) → 2 SO2 (g) + O2 (g) ΔH° = 198.2 kJ Find ΔH° for : 2 S(s) + 3 O2(g) → 2 SO3(g)

One method for making ethanol,C2H5OH,involves the gas-phase hydration of ethylene,C2H4: Estimate ΔH for this reaction from the given average bond dissociation energies,D.

Which equation represents the reaction whose ΔH,represents the standard enthalpy of formation of CHCl3(l) at 25°C? (i.e. ,for which is ΔH = ΔH°f of CHCl3)

Use the given standard enthalpies of formation to calculate ΔH° for the following reaction 3 Fe2O3(s) + CO(g) → 2 Fe3O4(s) + CO2(g) .

Calculate the enthalpy of combustion per mole for C6H12O6.Assume that the combustion products are CO2(g) and H2O(l) .

The values of ΔH°_f for the three states of benzene are approximately -22 kcal/mol,-11 kcal/mol,and Which is the value for solid benzene?

Given that ΔH°= -311 kJ for the hydrogenation of acetylene,C₂H₂: H-C C-H(g) + 2 H₂(g) → CH₃-CH₃(g) And the following bond dissociation energies,estimate a value for the C-to-C triple bond dissociation energy.

For the reaction 2CH₄ (g) + 3 Cl₂ (g) → 2 CHCl₃ (l) + 3 H₂ (g) ,ΔH° = -118.6 kJ. ΔH°_f = -134.1 kJ/mol for CHCl₃ (l) .Find ΔH°_f for CH₄ (g) .

Ethyl alcohol is produced by the fermentation of glucose,C₆H₁₂O₆. C₆H₁₂O₆(s) → 2 C₂H₅OH(l) + 2 CO₂(g) ΔH° = -69.1 kJ Given that the enthalpy of formation is -277.7 kJ/mol for C₂H₅OH(l) and -393.5 kJ/mol for CO₂(g) ,find the enthalpy of formation for C₆H₁₂O₆.

Determine the sign of ΔS° for each of the following: I.C₆H₆(s) → C₆H₆(l) II.2 SO₂(g) + O₂(g) → 2 SO₃(g)

Use the given average bond dissociation energies,D,to estimate ΔH for the reaction of methane,CH₄(g) ,with fluorine according to the equation: CH₄(g) + 2 F₂(g) → CF₄(g) + 2 H₂(g)

The heat of combustion per mole for acetylene,C₂H₂(g) ,is -1299.5 kJ/mol.Assuming that the combustion products are CO₂(g) and H₂O(l) ,and given that the enthalpy of formation is -393.5 kJ/mol for CO₂(g) and -285.8 kJ/mol for H₂O(l) ,find the enthalpy of formation of C₂H₂(g) .

Find ΔH° for the reaction C₃H₈(g) + 5 O₂(g) → 3 CO₂(g) + 4 H₂O(l) . ΔH° = -2046 kJ for the reaction: C₃H₈(g) + 5 O₂(g) → 3 CO₂(g) + 4 H₂O(g) The heat of vaporization of water is 44.0 kJ/mol.Note that H₂O is a liquid in the first reaction and a gas in the second.

For the reaction,C₂H₂(g) → 2 C(g) + 2 H(g) ,one would expect

Given: S (s) + O₂ (g) → SO₂ (g) ΔH° = -296.1 kJ 2 SO₃ (g) → 2 SO₂ (g) + O₂ (g) ΔH° = 198.2 kJ Find ΔH° for : 2 S(s) + 3 O₂(g) → 2 SO₃(g)

One method for making ethanol,C₂H₅OH,involves the gas-phase hydration of ethylene,C₂H₄: Estimate ΔH for this reaction from the given average bond dissociation energies,D.

Which equation represents the reaction whose ΔH,represents the standard enthalpy of formation of CHCl₃(l) at 25°C? (i.e. ,for which is ΔH = ΔH°_f of CHCl₃)

Use the given standard enthalpies of formation to calculate ΔH° for the following reaction 3 Fe₂O₃(s) + CO(g) → 2 Fe₃O₄(s) + CO₂(g) .

Calculate the enthalpy of combustion per mole for C₆H₁₂O₆.Assume that the combustion products are CO₂(g) and H₂O(l) .