Q: A 25.0 g sample of copper (Cs = 0.385 J/g·°C) is heated from 20.0 °C to 80.0 °C. How much heat is absorbed by the copper?

$$q = 25.0 \times 0.385 \times (80.0 - 20.0) = 577.5\ \text{J}$$

Q: Calculate the amount of heat released when 10.0 g of ethanol (Cs = 2.42 J/g·°C) cools from 50.0 °C to 25.0 °C.

$$q = 10.0 \times 2.42 \times (25.0 - 50.0) = -605\ \text{J}$$

Q: How much heat is evolved when 25.0 g of carbon (C, molar mass = 12.01 g/mol) is burned? ($$\Delta H_{combustion} = -395.4\ \text{kJ/mol})$$

$$q = (25.0/12.01) \times (-395.4) = -823\ \text{kJ}$$

Q: Which of the following is the correct formation equation for CaCO$$_3(s$$)?

$$\text{Ca}(s) + \text{C}(s, \text{graphite}) + \frac{3}{2} \text{O}_2(g) \rightarrow \text{CaCO}_3(s)$$

Q: Given the reaction: $$2\ \text{C}_2\text{H}_2(g) + 5\ \text{O}_2(g) \rightarrow 4\ \text{CO}_2(g) + 2\ \text{H}_2\text{O}(l)$$, and the following standard enthalpies of formation: $$\Delta H_f^\circ(\text{CO}_2) = -393.5\ \text{kJ/mol}$$, $$\Delta H_f^\circ(\text{H}_2\text{O}) = -285.8\ \text{kJ/mol}$$, $$\Delta H_f^\circ(\text{C}_2\text{H}_2) = 227.4\ \text{kJ/mol}$$, $$\Delta H_f^\circ(\text{O}_2) = 0$$, what is $$\Delta H_{rxn}$$?

$$\Delta H_{rxn} = [(4 \times -393.5) + (2 \times -285.8)] - [2 \times 227.4 + 5 \times 0] = -2600\ \text{kJ}$$

Question 1

Which of the following best describes a state function, as illustrated by the change in altitude when climbing a mountain?

Accepted Answer

A property that depends only on the initial and final states, not the path taken.

Question 2

A 25.0 g sample of copper (Cs = 0.385 J/g·°C) is heated from 20.0 °C to 80.0 °C. How much heat is absorbed by the copper?

Accepted Answer

$$q = 25.0 	imes 0.385 	imes (80.0 - 20.0) = 577.5\ 	ext{J}$$

Question 3

Which of the following substances would require the most energy to raise the temperature of 10.0 g by 10.0 °C?

Accepted Answer

Water (Cs = 4.18 J/g·°C)

Question 4

A 50.0 g piece of iron (Cs = 0.449 J/g·°C) at 100.0 °C is placed in 100.0 g of water at 20.0 °C. What is the direction of heat flow?

Accepted Answer

Heat flows from the iron to the water.

Question 5

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

Accepted Answer

$$\Delta E = q + w$$

Question 6

A chemical reaction in a coffee-cup calorimeter causes the temperature of the solution to increase. What can you conclude about the reaction?

Accepted Answer

The reaction is exothermic.

Question 7

Calculate the amount of heat released when 10.0 g of ethanol (Cs = 2.42 J/g·°C) cools from 50.0 °C to 25.0 °C.

Accepted Answer

$$q = 10.0 	imes 2.42 	imes (25.0 - 50.0) = -605\ 	ext{J}$$

Question 8

Which of the following statements about the first law of thermodynamics is correct?

Accepted Answer

The total energy of the universe is constant.

Question 9

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

Accepted Answer

The reaction is endothermic and absorbs heat from the surroundings.

Question 10

How much heat is evolved when 25.0 g of carbon (C, molar mass = 12.01 g/mol) is burned? ($$\Delta H_{combustion} = -395.4\ 	ext{kJ/mol})$$

Accepted Answer

$$q = (25.0/12.01) 	imes (-395.4) = -823\ 	ext{kJ}$$

Question 11

Which of the following is the correct formation equation for CaCO$$_3(s$$)?

Accepted Answer

$$	ext{Ca}(s) + 	ext{C}(s, 	ext{graphite}) + \frac{3}{2} 	ext{O}_2(g) ightarrow 	ext{CaCO}_3(s)$$

Question 12

Given the reaction: $$2\ 	ext{C}_2	ext{H}_2(g) + 5\ 	ext{O}_2(g) ightarrow 4\ 	ext{CO}_2(g) + 2\ 	ext{H}_2	ext{O}(l)$$, and the following standard enthalpies of formation: $$\Delta H_f^\circ(	ext{CO}_2) = -393.5\ 	ext{kJ/mol}$$, $$\Delta H_f^\circ(	ext{H}_2	ext{O}) = -285.8\ 	ext{kJ/mol}$$, $$\Delta H_f^\circ(	ext{C}_2	ext{H}_2) = 227.4\ 	ext{kJ/mol}$$, $$\Delta H_f^\circ(	ext{O}_2) = 0$$, what is $$\Delta H_{rxn}$$?

Accepted Answer

$$\Delta H_{rxn} = [(4 	imes -393.5) + (2 	imes -285.8)] - [2 	imes 227.4 + 5 	imes 0] = -2600\ 	ext{kJ}$$

Question 13

If a reaction is reversed, what happens to the sign of $$\Delta H$$?

Accepted Answer

The sign of $$\Delta H is $$reversed.

Question 14

A 100.0 g sample of water at 80.0 °C is mixed with 100.0 g of water at 20.0 °C in an insulated container. What is the final temperature, assuming no heat is lost to the surroundings?

Accepted Answer

50.0 °C

Question 15

Which of the following best explains why water is used as a coolant in car engines?

Accepted Answer

Water has a high specific heat capacity, so it can absorb a lot of heat without a large temperature increase.

Question 16

A coffee-cup calorimeter is used to measure the enthalpy change of a reaction. Which of the following is true about the system and surroundings in this setup?

Accepted Answer

The reaction mixture is the system, and the water in the calorimeter is the surroundings.

Question 17

Which of the following energy sources has shown the greatest increase in consumption since 1950, according to the provided graph?

Accepted Answer

Petroleum

Question 18

The increase in atmospheric carbon dioxide concentration over the past 50 years is most closely linked to which of the following?

Accepted Answer

Increased combustion of fossil fuels

Thermochemistry: Energy, Heat, and Chemical Reactions

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