Q: A chemical reaction occurs in a calorimeter at constant pressure. Which equation should be used to calculate the heat flow?

$$q = m \times c \times \Delta T$$

Question 1

Which of the following statements best describes the First Law of Thermodynamics?

Accepted Answer

Energy cannot be created or destroyed, only transformed from one form to another.

Question 2

A chemical reaction occurs in a calorimeter at constant pressure. Which equation should be used to calculate the heat flow?

Accepted Answer

$$q = m 	imes c 	imes \Delta T$$

Question 3

Which of the following processes will result in an increase in entropy ($$\Delta S \u003e 0$$)?

Accepted Answer

Dissolving NaCl in water.

Question 4

Given the reaction: $$2H_2(g) + O_2$(g) \rightarrow 2H_2O(l)$$, which of the following is true about the entropy change ($$\Delta S$$)?

Accepted Answer

$$\Delta S is $$negative because the number of gas molecules decreases.

Question 5

Which formula is used to calculate the standard entropy change for a chemical reaction?

Accepted Answer

$$\Delta S^\circ_{rxn} = \sum S^\circ_{products} - \sum S^\circ_{reactants}$$

Question 6

A student mixes two solutions and observes that the temperature of the mixture decreases. What can be concluded about the enthalpy change ($$\Delta H) of $$the process?

Accepted Answer

$$\Delta H is $$positive; the process is endothermic.

Question 7

Which of the following is the correct expression for Gibbs free energy change?

Accepted Answer

$$\Delta G = \Delta H - T\Delta S$$

Question 8

For a reaction at equilibrium, which of the following is true?

Accepted Answer

$$\Delta G = 0$$

Question 9

Which of the following changes will always increase the entropy of a system?

Accepted Answer

Melting a solid to a liquid.

Question 10

A reaction has $$\Delta H = -100 kJ $$and $$\Delta S = -200 J/K. At $$what temperature will the reaction become non-spontaneous?

Accepted Answer

$$T \u003e 500 K$$

Question 11

Which of the following is NOT a state function?

Accepted Answer

Work ($$w)$$

Question 12

Which of the following best explains why mixing two gases increases entropy?

Accepted Answer

The number of possible microstates increases.

Question 13

Which equation would you use to calculate the entropy change for heating a substance at constant pressure?

Accepted Answer

$$\Delta S = q_{rev}/T$$

Question 14

Which of the following statements about spontaneous processes is correct?

Accepted Answer

A spontaneous process always has $$\Delta G \u003c 0.$$

Question 15

If a reaction has $$\Delta H \u003e 0$$ and $$\Delta S \u003e 0$$, under what condition will it be spontaneous?

Accepted Answer

At high temperatures.

Question 16

Which of the following is the correct formula for calculating the standard free energy change from equilibrium constant $$K$$?

Accepted Answer

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

Question 17

Which of the following will result in the largest increase in entropy?

Accepted Answer

Evaporation of water.

Question 18

A reaction has $$\Delta H = -50 kJ $$and $$\Delta S = 100 J/K. Is $$the reaction spontaneous at $$T = 298 K$$?

Accepted Answer

Yes, because $$\Delta G \u003c 0.$$

Question 19

Which of the following is true about the entropy of a pure, perfectly crystalline substance at absolute zero?

Accepted Answer

Its entropy is zero.

Thermodynamics and Spontaneous Changes: Entropy, Free Energy, and Equilibrium

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