Question 1

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

Accepted Answer

Energy can be converted from one form to another, but it is neither created nor destroyed.

Question 2

A chemical reaction occurs in a closed system where the system loses 850 J of heat to the surroundings and the surroundings do 200 J of work on the system. What is the change in internal energy ($$\Delta E) of $$the system?

Accepted Answer

$$\Delta E = -650\ \mathrm{J}$$

Question 3

Which of the following is NOT a state function?

Accepted Answer

Work ($$w)$$

Question 4

What is the correct mathematical relationship for the change in internal energy of a system?

Accepted Answer

$$\Delta E = q + w$$

Question 5

Which of the following processes is exothermic?

Accepted Answer

Combustion of butane ($$\mathrm{C_4H_{10}})$$

Question 6

A reaction is carried out in a coffee-cup calorimeter. If the temperature of the solution increases, what can be concluded about the reaction?

Accepted Answer

The reaction is exothermic and $$\Delta H \u003c 0.$$

Question 7

Which equation correctly defines enthalpy ($$H$$)?

Accepted Answer

$$H = E + PV$$

Question 8

Calculate the work done (in J) when a gas expands from 0.300 L to 1.200 L against a constant external pressure of 1.00 atm. ($$1\ \mathrm{L \cdot atm} = 101.3\ \mathrm{J})$$

Accepted Answer

$$w = -91.3\ \mathrm{J}$$

Question 9

Which of the following statements about enthalpy is FALSE?

Accepted Answer

The enthalpy change for a reaction is the same for the reverse reaction.

Question 10

Given the reaction $$2\mathrm{H_2O_2}(l) \rightarrow 2\mathrm{H_2O}(l) + \mathrm{O_2$}(g)$$ with $$\Delta H = -196\ \mathrm{kJ}$$, how much heat is released when 10.0 g of $$\mathrm{H_2O_2}$$ decomposes? (Molar mass $$\mathrm{H_2O_2} = 34.0\ \mathrm{g/mol})$$

Accepted Answer

$$-28.8\ \mathrm{kJ}$$

Question 11

Which of the following best describes an isolated system?

Accepted Answer

It cannot exchange heat or mass with its surroundings.

Question 12

Which of the following is true for a process where $$q \u003e 0$$ and $$w \u003c 0$$?

Accepted Answer

The system gains heat and does work on the surroundings.

Question 13

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

Accepted Answer

Melting of ice

Question 14

A bomb calorimeter is used to measure the heat of combustion of a sample. If the temperature of the water increases, what is the sign of $$q_{rxn}$$?

Accepted Answer

$$q_{rxn} \u003c 0$$

Question 15

Which of the following is the correct expression for the enthalpy change of a reaction using standard enthalpies of formation?

Accepted Answer

$$\Delta H$$^{\circ}$$_{rxn} = \sum n \Delta H$$^{\circ}$$_f (	ext{products}) - \sum m \Delta H$$^{\circ}$$_f (	ext{reactants})$$

Question 16

Which of the following statements about bond enthalpy is correct?

Accepted Answer

Bond enthalpy is always positive because energy is required to break bonds.

Question 17

Using the following average bond enthalpies: $$\mathrm{C-H} = 413\ \mathrm{kJ/mol}$$, $$\mathrm{O=O} = 495\ \mathrm{kJ/mol}$$, $$\mathrm{C=O} = 799\ \mathrm{kJ/mol}$$, $$\mathrm{O-H} = 463\ \mathrm{kJ/mol}$$, estimate $$\Delta H$$ for the combustion of methane: $$\mathrm{CH_4$} + 2\mathrm{O_2$} \rightarrow \mathrm{CO_2$} + 2\mathrm{H_2O} ($$all species gaseous).

Accepted Answer

$$\Delta H = -802\ \mathrm{kJ}$$

Question 18

Which of the following best explains why $$q$$ and $$w$$ are not state functions?

Accepted Answer

They depend on the path taken between the initial and final states.

Chapter 5: Thermochemistry – Study Notes for General Chemistry

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