$$\Delta E = E_{\text{final}} - E_{\text{initial}}$$

$$q = 100 \times 4.18 \times 50 = 20,900 \text{ J}$$

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

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. Which of the following statements is TRUE?

Accepted Answer

The system can exchange only heat, not mass, with its surroundings.

Question 3

Which equation correctly represents the change in internal energy of a system?

Accepted Answer

$$\Delta E = E_{	ext{final}} - E_{	ext{initial}}$$

Question 4

If a system absorbs heat from its surroundings and has work done on it, what is the sign of $$q$$, $$w$$, and $$\Delta E$$?

Accepted Answer

$$q is $$positive, $$w is $$positive, $$\Delta E is $$positive

Question 5

Which of the following is a state function?

Accepted Answer

Internal energy ($$E)$$

Question 6

What is the correct formula for calculating the electrostatic potential energy between two charged particles?

Accepted Answer

$$E_{el} = \frac{kQ_1Q_2}{d}$$

Question 7

Which process is exothermic?

Accepted Answer

Combustion of butane

Question 8

A reaction occurs at constant pressure and releases heat to the surroundings. Which statement is correct?

Accepted Answer

The enthalpy change ($$\Delta H) is $$negative and the reaction is exothermic.

Question 9

Which of the following is TRUE about enthalpy ($$H$$)?

Accepted Answer

Enthalpy is a state function and an extensive property.

Question 10

Calculate the heat required to raise the temperature of 100 g of water from 25°C to 75°C. (Specific heat of water $$C_s = 4.18 	ext{ J/g K})$$

Accepted Answer

$$q = 100 	imes 4.18 	imes 50 = 20,900 	ext{ J}$$

Question 11

Which calorimeter is used to measure heat changes at constant volume?

Accepted Answer

Bomb calorimeter

Question 12

According to Hess's Law, which statement is correct?

Accepted Answer

The enthalpy change of a reaction is the same whether it occurs in one step or multiple steps.

Question 13

Which of the following best describes the standard enthalpy of formation ($$\Delta H_f^\circ$$)?

Accepted Answer

The enthalpy change when one mole of a compound is formed from its elements in their standard states.

Question 14

Which equation is used to calculate the enthalpy change of a reaction using enthalpies of formation?

Accepted Answer

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

Question 15

Which statement about bond enthalpy is correct?

Accepted Answer

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

Question 16

A reaction has a positive enthalpy change ($$\Delta H \u003e 0). $$Which of the following is TRUE?

Accepted Answer

The reaction is endothermic and absorbs heat.

Question 17

Which of the following is a real-world example of energy conversion involving chemical reactions?

Accepted Answer

A lamp converting electrical energy to radiant and heat energy.

Question 18

Which of the following statements about the Earth as a system is correct?

Accepted Answer

Earth is a closed system because it exchanges energy but not significant mass with space.

Thermochemistry: Energy Changes in Chemical Reactions

Study Guide - Practice Questions