Question 1

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

Accepted Answer

The total amount of energy in the universe is constant; energy can only be transferred or transformed.

Question 2

A 50.0 g block of metal at 80.0°C is placed in 100.0 g of water at 25.0°C. The final temperature is 30.0°C. If the specific heat of water is $$4.18\ \mathrm{J/(g\cdot°C)}$$, what is the specific heat capacity of the metal? (Assume no heat is lost to the surroundings.)

Accepted Answer

$$0.42\ \mathrm{J/(g\cdot°C)}$$

Question 3

Which of the following is an example of potential energy?

Accepted Answer

A compressed spring

Question 4

Calculate the amount of heat required to raise the temperature of 250 g of water from 20.0°C to 50.0°C. ($$C_s$$ for water = $$4.18\ \mathrm{J/(g\cdot°C)})$$

Accepted Answer

$$31,350\ \mathrm{J}$$

Question 5

Which equation correctly relates the change in internal energy ($$\Delta E) of a $$system to heat ($$q) $$and work ($$w$$)?

Accepted Answer

$$\Delta E = q + w$$

Question 6

A balloon is inflated from 0.500 L to 2.00 L against an external pressure of 1.00 atm. How much work is done by the gas? ($$1\ \mathrm{L\cdot atm} = 101.3\ \mathrm{J})$$

Accepted Answer

$$-152\ \mathrm{J}$$

Question 7

Which of the following processes is exothermic?

Accepted Answer

Combustion of gasoline in a car engine

Question 8

Given the following reactions and their enthalpy changes:

$$\mathrm{C(s) + O_2$(g) \rightarrow CO_2$(g)}\ \Delta H = -393.5\ \mathrm{kJ}$$
$$\mathrm{2H_2(g) + O_2$(g) \rightarrow 2H_2O(g)}\ \Delta H = -483.6\ \mathrm{kJ}$$
$$\mathrm{CH_4$(g) + 2O_2(g) \rightarrow CO_2$(g) + 2H_2O(g)}\ \Delta H = -802.5\ \mathrm{kJ}$$

What is the enthalpy of formation ($$\Delta H_f) $$for methane, $$\mathrm{CH_4$(g)}$$?

Accepted Answer

$$-74.6\ \mathrm{kJ/mol}$$

Question 9

Which of the following best explains why the lattice energy of $$\mathrm{MgO} is $$greater than that of $$\mathrm{NaCl}$$?

Accepted Answer

$$\mathrm{Mg$$^{2+}$$}$$ and $$\mathrm{O$$^{2-}$$}$$ have higher charges than $$\mathrm{Na^+}$$ and $$\mathrm{Cl^-}.$$

Question 10

Which of the following is true about state functions?

Accepted Answer

They depend only on the initial and final states, not on the path taken.

Question 11

A reaction is carried out in a bomb calorimeter and the temperature of the water increases. What can be concluded about the reaction?

Accepted Answer

The reaction is exothermic and releases energy to the surroundings.

Question 12

Which of the following equations correctly expresses Hess’s Law for the enthalpy change of a reaction?

Accepted Answer

$$\Delta H_{rxn} = \sum \Delta H_{steps}$$

Question 13

Which of the following best describes the sign conventions for $$q$$, $$w$$, and $$\Delta E in $$thermochemistry?

Accepted Answer

$$q is $$positive when heat is absorbed by the system, $$w is $$positive when work is done on the system, $$\Delta E is $$positive when energy flows into the system.

Question 14

Which of the following reactions is an example of an endothermic process?

Accepted Answer

Photosynthesis in plants

Question 15

Calculate the enthalpy change for the reaction $$2\mathrm{C_2H_2(g)} + 5\mathrm{O_2$(g)} \rightarrow 4\mathrm{CO_2$(g)} + 2\mathrm{H_2O(l)}$$ using the following standard enthalpies of formation:

$$\Delta H_f^\circ [\mathrm{C_2H_2(g)}] = +227.4\ \mathrm{kJ/mol}$$
$$\Delta H_f^\circ [\mathrm{CO_2$(g)}] = -393.5\ \mathrm{kJ/mol}$$
$$\Delta H_f^\circ [\mathrm{H_2O(l)}] = -285.8\ \mathrm{kJ/mol}$$

Accepted Answer

$$-2600.4\ \mathrm{kJ}$$

Question 16

Which of the following best describes the relationship between bond energy and bond strength?

Accepted Answer

The higher the bond energy, the stronger the bond.

Question 17

Which of the following statements about the standard enthalpy of formation ($$\Delta H_f^\circ) is $$correct?

Accepted Answer

$$\Delta H_f^\circ$$ for any element in its standard state is zero.

Question 18

Which of the following factors will increase the lattice energy of an ionic compound?

Accepted Answer

Increasing the charge of the ions

Chapter 9: Thermochemistry – Energy, Heat, and Work in Chemical Reactions

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