Q: A 0.015 kg ball is dropped from a height of 10.0 m. What is its potential energy at the top? $$(g = 9.8 \ \mathrm{m/s^2$})$$

$$PE = mgh = 0.015 \times 9.8 \times 10.0 = 1.47 \ \mathrm{J}$$

Q: If a 250.0 g sample of copper ($$c = 0.385 \ \mathrm{J/g \cdot ^\circ C}) $$absorbs 2.50 J of heat, what is the temperature change?

$$\Delta T = \frac{q}{mc} = \frac{2.50}{250.0 \times 0.385} = 0.026 \ ^\circ \mathrm{C}$$

Q: A sample of 120.0 g H$$_2O $$cools from 90 $$^\circC to 45$$ $$^\circC. $$How much heat (in kJ) is released? ($$c = 4.184 \ \mathrm{J/g \cdot ^\circ C})$$

$$q = mc\Delta T = 120.0 \times 4.184 \times (45 - 90) = -22,555 \ \mathrm{J} = -22.6 \ \mathrm{kJ}$$

Q: A refrigerator uses 780 kWh of electrical energy per year. How many kilocalories does it use in three years? ($$1 \ \mathrm{kWh} = 860 \ \mathrm{kcal})$$

$$780 \times 3 \times 860 = 2,010,600 \ \mathrm{kcal}$$

Q: A 50.0 g heated metal is placed into 822.5 g of water. The metal heats up the water to 32.08 $$^\circC $$and releases 14.55 kJ of energy. What is the initial temperature of the water? ($$c_{H_2O} = 4.184 \ \mathrm{J/g \cdot ^\circ C})$$

$$q = mc\Delta T \rightarrow 14,550 = 822.5 \times 4.184 \times (32.08 - T_i) \rightarrow T_i = 29.7 \ ^\circ \mathrm{C}$$

Question 1

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

Accepted Answer

Energy can be transferred between system and surroundings, but cannot be created or destroyed.

Question 2

A 0.015 kg ball is dropped from a height of 10.0 m. What is its potential energy at the top? $$(g = 9.8 \ \mathrm{m/s^2$})$$

Accepted Answer

$$PE = mgh = 0.015 	imes 9.8 	imes 10.0 = 1.47 \ \mathrm{J}$$

Question 3

Which of the following processes is an example of an endothermic reaction?

Accepted Answer

Water boiling

Question 4

If a 250.0 g sample of copper ($$c = 0.385 \ \mathrm{J/g \cdot ^\circ C}) $$absorbs 2.50 J of heat, what is the temperature change?

Accepted Answer

$$\Delta T = \frac{q}{mc} = \frac{2.50}{250.0 	imes 0.385} = 0.026 \ ^\circ \mathrm{C}$$

Question 5

Which formula is used to calculate the kinetic energy of a moving object?

Accepted Answer

$$KE = \frac{1}{2}mv^2$

Question 6

A sample of 120.0 g H$$_2O $$cools from 90 $$^\circC to 45$$ $$^\circC. $$How much heat (in kJ) is released? ($$c = 4.184 \ \mathrm{J/g \cdot ^\circ C})$$

Accepted Answer

$$q = mc\Delta T = 120.0 	imes 4.184 	imes (45 - 90) = -22,555 \ \mathrm{J} = -22.6 \ \mathrm{kJ}$$

Question 7

Which of the following is true about exothermic reactions?

Accepted Answer

They release heat to the surroundings.

Question 8

A coffee-cup calorimeter contains 90.0 g H$$_2O at 30.0$$ $$^\circC. 60.0 g of $$lead at 68.3 $$^\circC is $$added, and the final temperature is 48.0 $$^\circC. $$What is the heat capacity of the calorimeter? ($$c_{Pb} = 0.128 \ \mathrm{J/g \cdot ^\circ C}$$, $$c_{H_2O} = 4.184 \ \mathrm{J/g \cdot ^\circ C})$$

Accepted Answer

The heat capacity of the calorimeter is negligible based on the information provided.

Question 9

Which equation correctly relates heat ($$q$$), mass ($$m$$), specific heat ($$c$$), and temperature change ($$\Delta T$$)?

Accepted Answer

$$q = mc\Delta T$$

Question 10

A refrigerator uses 780 kWh of electrical energy per year. How many kilocalories does it use in three years? ($$1 \ \mathrm{kWh} = 860 \ \mathrm{kcal})$$

Accepted Answer

$$780 	imes 3 	imes 860 = 2,010,600 \ \mathrm{kcal}$$

Question 11

Which of the following statements deals with potential energy with nonchemical energy associated?

Accepted Answer

Your chemistry book sitting on a table counter near the trashcan weighing 12 N at a height of 1.2 m.

Question 12

A 15.7 g sample of silver raises its temperature by 17.2 $$^\circC $$when it absorbs 684.5 J of energy. What is its molar heat capacity? (Molar mass of Ag = 107.87 g/mol)

Accepted Answer

$$C_{molar} = \frac{q}{n\Delta T} = \frac{684.5}{(15.7/107.87) 	imes 17.2} = 286 \ \mathrm{J/mol \cdot ^\circ C}$$

Question 13

Which of the following substances would show the greatest temperature change upon absorbing 2.50 J of heat? (Refer to the specific heat capacities: Al = 0.900, Cu = 0.385, ethanol = 2.460, wood = 1.760 $$\mathrm{J/g \cdot ^\circ C})$$

Accepted Answer

250.0 g Cu

Question 14

A 50.0 g heated metal is placed into 822.5 g of water. The metal heats up the water to 32.08 $$^\circC $$and releases 14.55 kJ of energy. What is the initial temperature of the water? ($$c_{H_2O} = 4.184 \ \mathrm{J/g \cdot ^\circ C})$$

Accepted Answer

$$q = mc\Delta T ightarrow 14,550 = 822.5 	imes 4.184 	imes (32.08 - T_i) ightarrow T_i = 29.7 \ ^\circ \mathrm{C}$$

Question 15

What is the standard heat capacity (in kJ/$$^\circC) of a $$calorimeter that absorbs 87.0 J as its temperature goes from 33 $$^\circC to 38.1$$ $$^\circC$$?

Accepted Answer

$$C = \frac{q}{\Delta T} = \frac{87.0}{38.1 - 33} = 17.1 \ \mathrm{J/^\circ C} = 0.0171 \ \mathrm{kJ/^\circ C}$$

Question 16

Which of the following best describes the difference between heat and work in thermochemistry?

Accepted Answer

Heat is the transfer of energy due to temperature difference, while work is the transfer of energy due to force acting over a distance.

Question 17

A gas expands from 4.3 L to 8.2 L at a constant pressure of 931 mmHg, absorbing 2.34 kJ of energy. What is the change in internal energy of the system? ($$1 \ \mathrm{atm} = 760 \ \mathrm{mmHg}$$, $$1 \ \mathrm{L \cdot atm} = 101.3 \ \mathrm{J})$$

Accepted Answer

$$\Delta E = q + w = 2,340 \ \mathrm{J} + [-(931/760) 	imes (8.2 - 4.3) 	imes 101.3] = 2,340 + (-505) = 1,835 \ \mathrm{J}$$

Thermochemistry and Heat Capacity: Study Notes for General Chemistry

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