Q: A 50.0 g sample of metal at $$100\ ^\circ\mathrm{C} is $$placed in 100.0 g of water at $$25.0\ ^\circ\mathrm{C}. $$The final temperature is $$30.0\ ^\circ\mathrm{C}. If $$the specific heat of water is $$4.184\ \mathrm{J/g\cdot K}$$, what is the amount of heat lost by the metal?

$$q = 100.0\ \mathrm{g} \times 4.184\ \mathrm{J/g\cdot K} \times (30.0 - 25.0)\ \mathrm{K} = 2092\ \mathrm{J}$$

Q: Calculate the work done by a gas that expands from $$2.0\ \mathrm{L} to$$ $$5.0\ \mathrm{L}$$ against a constant external pressure of $$1.5\ \mathrm{atm}$$. ($$1\ \mathrm{L\cdot atm} = 101.3\ \mathrm{J})$$

$$w = -P_{ext} \Delta V = -1.5\ \mathrm{atm} \times (5.0 - 2.0)\ \mathrm{L} = -4.5\ \mathrm{L\cdot atm} = -456\ \mathrm{J}$$

Question 1

Which of the following statements best describes an exothermic process?

Accepted Answer

The system releases heat to the surroundings, resulting in a negative $$q.$$

Question 2

A 50.0 g sample of metal at $$100\ ^\circ\mathrm{C} is $$placed in 100.0 g of water at $$25.0\ ^\circ\mathrm{C}. $$The final temperature is $$30.0\ ^\circ\mathrm{C}. If $$the specific heat of water is $$4.184\ \mathrm{J/g\cdot K}$$, what is the amount of heat lost by the metal?

Accepted Answer

$$q = 100.0\ \mathrm{g} 	imes 4.184\ \mathrm{J/g\cdot K} 	imes (30.0 - 25.0)\ \mathrm{K} = 2092\ \mathrm{J}$$

Question 3

Which of the following phase changes is typically endothermic and involves an increase in entropy?

Accepted Answer

Sublimation of dry ice (solid $$\mathrm{CO}_2) to $$gas

Question 4

Given the reaction: $$\mathrm{C(graphite) + O_2$(g) \rightarrow CO_2$(g)}$$ with $$\Delta H = -393.5\ \mathrm{kJ}$$, what does the negative sign of $$\Delta H$$ indicate?

Accepted Answer

The reaction is exothermic and releases heat to the surroundings.

Question 5

Which of the following best describes a state function?

Accepted Answer

A property that depends only on the initial and final states of a system, not on the path taken.

Question 6

Calculate the work done by a gas that expands from $$2.0\ \mathrm{L} to$$ $$5.0\ \mathrm{L}$$ against a constant external pressure of $$1.5\ \mathrm{atm}$$. ($$1\ \mathrm{L\cdot atm} = 101.3\ \mathrm{J})$$

Accepted Answer

$$w = -P_{ext} \Delta V = -1.5\ \mathrm{atm} 	imes (5.0 - 2.0)\ \mathrm{L} = -4.5\ \mathrm{L\cdot atm} = -456\ \mathrm{J}$$

Question 7

Which of the following statements about entropy ($$\Delta S) is $$correct?

Accepted Answer

$$\Delta S$$ measures the change in disorder or randomness of a system.

Question 8

Which process would you expect to have the largest increase in entropy?

Accepted Answer

Sublimation of iodine

Question 9

A chemical reaction has $$\Delta H = +25\ \mathrm{kJ}$$ and $$\Delta S = +100\ \mathrm{J/K}. At $$what temperature will the reaction become spontaneous? ($$\Delta G = \Delta H - T\Delta S)$$

Accepted Answer

$$T \u003e 250\ \mathrm{K}$$

Question 10

Which of the following best explains why the dissolution of ammonium nitrate in water is endothermic but spontaneous at room temperature?

Accepted Answer

The process is driven by a large positive entropy change ($$\Delta S) $$that outweighs the positive enthalpy change ($$\Delta H).$$

Question 11

Which of the following is true for a reaction at equilibrium?

Accepted Answer

$$\Delta G = 0$$

Question 12

Given the reaction $$2\mathrm{H}_2(g) + O_2$(g) \rightarrow 2\mathrm{H}_2O(l)$$, which of the following statements about entropy is correct?

Accepted Answer

The entropy of the system decreases because liquid water has fewer degrees of freedom than the gases.

Question 13

Which of the following is the correct expression for the standard Gibbs free energy change in terms of the equilibrium constant $$K$$?

Accepted Answer

$$\Delta G^\circ = -RT \ln K$$

Question 14

Which of the following best describes the effect of temperature on the spontaneity of an endothermic reaction with a positive entropy change?

Accepted Answer

The reaction becomes more spontaneous as temperature increases.

Question 15

Which of the following statements about bond dissociation enthalpy is correct?

Accepted Answer

Bond breaking is always endothermic because energy is required to break bonds.

Question 16

A reaction has $$\Delta H = -100\ \mathrm{kJ}$$ and $$\Delta S = -200\ \mathrm{J/K}. At $$what temperature will the reaction change from spontaneous to nonspontaneous?

Accepted Answer

$$T = 500\ \mathrm{K}$$

Question 17

Which of the following is a correct statement about the entropy change ($$\Delta S) $$for the freezing of water?

Accepted Answer

$$\Delta S is $$negative because the system becomes more ordered.

Question 18

Which of the following best explains why the entropy of a gas is higher than that of a solid?

Accepted Answer

Gas particles have more degrees of freedom and can move more randomly than solid particles.

Question 19

Which of the following is true for a spontaneous process at constant temperature and pressure?

Accepted Answer

$$\Delta G \u003c 0$$

Thermochemistry and Spontaneity: Energy, Enthalpy, Entropy, and Free Energy

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