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

$$\Delta H^\circ = \sum n \Delta H_f^\circ(\text{products}) - \sum m \Delta H_f^\circ(\text{reactants})$$

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 and releases heat to the surroundings. Which of the following statements is correct?

Accepted Answer

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

Question 3

Which of the following is a state function?

Accepted Answer

Internal energy ($$E)$$

Question 4

A gas expands against a constant external pressure of 2.00 atm from 5.00 L to 10.00 L. Calculate the work done by the system. ($$1 	ext{ L} \cdot 	ext{atm} = 101.3 	ext{ J})$$

Accepted Answer

$$w = -1013 	ext{ J}$$

Question 5

Which of the following best describes an isolated system?

Accepted Answer

It cannot exchange heat or mass with its surroundings.

Question 6

The specific heat of water is $$4.184 	ext{ J/g} \cdot 	ext{K}. $$How much heat is required to raise the temperature of $$50.0 	ext{ g} of $$water from $$20.0^\circ 	ext{C} to$$ $$30.0^\circ 	ext{C}$$?

Accepted Answer

$$2092 	ext{ J}$$

Question 7

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 8

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

Accepted Answer

$$\Delta E = q + w$$

Question 9

A reaction is carried out in a bomb calorimeter. Which thermodynamic quantity is most directly measured?

Accepted Answer

Change in internal energy ($$\Delta E)$$

Question 10

Which of the following is an extensive property?

Accepted Answer

Mass

Question 11

Given the following standard enthalpies of formation: $$\Delta H_f^\circ(CO$_2(g)) = -393.5$ kJ/mol, $$\Delta H_f^\circ$$(H_2$O(l)) = -285.8 kJ/$$mol, $$\Delta H_f^\circ(C$_6H$_{12}O$_6(s)) = -1273$ kJ/mol. Calculate $$\Delta H^\circ$$ for the combustion of glucose:

$$\mathrm{C_6H_{12}$$O_6(s) + 6$$ $$O_2(g$$) \rightarrow 6 $$CO_2(g) + 6 H_2O(l$$)}$

Accepted Answer

$$-2803 	ext{ kJ}$$

Question 12

Which of the following best explains why the enthalpy change for a reaction is equal in magnitude but opposite in sign for the reverse reaction?

Accepted Answer

Because enthalpy is a state function.

Question 13

A reaction has $$\Delta H = +150 	ext{ kJ}. $$Which of the following statements is true?

Accepted Answer

The reaction is endothermic and absorbs heat.

Question 14

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

Accepted Answer

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

Question 15

Which of the following best describes the energy changes when a chemical bond is formed?

Accepted Answer

Energy is released and the process is exothermic.

Question 16

A sample of ethanol ($$C_2H_5OH) is $$combusted in a bomb calorimeter. The temperature of the water increases. Which of the following is true?

Accepted Answer

The reaction is exothermic and $$q is $$negative for the system.

Question 17

Which of the following is NOT a renewable energy source?

Accepted Answer

Coal

Question 18

Which of the following statements about calorimetry is correct?

Accepted Answer

A coffee-cup calorimeter measures heat at constant pressure.

Question 19

Which of the following foods provides the highest energy per gram when combusted?

Accepted Answer

Fats

Chapter 5: Thermochemistry – Study Notes for General Chemistry

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