Q: A refrigerator uses 700 kWh of electrical energy per year. How many joules of energy does this represent? ($$1 \ \mathrm{kWh} = 3.60 \times 10^6$ \ \mathrm{J})$$

$$2.52 \times 10^9$ \ \mathrm{J}$$

Q: A reaction occurs at constant pressure. If the system absorbs 72.4 kJ of heat and the volume compresses from 15.0 L to 5.0 L against a constant pressure of 2.0 atm, what is the change in internal energy ($$\Delta E$$)? ($$1 \mathrm{L} \cdot \mathrm{atm} = 101.3 \ \mathrm{J})$$

$$\Delta E = 72.4 \ \mathrm{kJ} + 2.0 \times (5.0 - 15.0) \times 101.3 \ \mathrm{J}$$

Question 1

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

Accepted Answer

Energy can be transformed between system and surroundings, but the total energy of the universe remains constant.

Question 2

A sample of 15.0 g of water absorbs 627 J of heat. What is the temperature change of the water? (Specific heat capacity of water = $$4.18 \ \mathrm{J} / \mathrm{g} \cdot ^\circ \mathrm{C})$$

Accepted Answer

$$\Delta T = 10.0^\circ \mathrm{C}$$

Question 3

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

Accepted Answer

Dry ice subliming

Question 4

A metal block weighing 1.50 kg is lifted to a height of 120.0 meters above the ground. What is its potential energy? ($$g = 9.8 \ \mathrm{m}/\mathrm{s}^2)$$

Accepted Answer

$$PE = 1,764 \ \mathrm{J}$$

Question 5

Which of the following substances would show the greatest temperature change upon absorbing 25.0 J of heat? (Assume equal masses)

Accepted Answer

Copper ($$c = 0.385 \ \mathrm{J}/\mathrm{g} \cdot ^\circ \mathrm{C})$$

Question 6

A refrigerator uses 700 kWh of electrical energy per year. How many joules of energy does this represent? ($$1 \ \mathrm{kWh} = 3.60 	imes 10^6$ \ \mathrm{J})$$

Accepted Answer

$$2.52 	imes 10^9$ \ \mathrm{J}$$

Question 7

Which of the following is true about heat capacity?

Accepted Answer

The temperature change of an object is inversely proportional to its heat capacity.

Question 8

A chemical reaction occurs in a bomb calorimeter. If 12.13 g of a substance is burned and the temperature of the calorimeter increases by $$15.2^\circ \mathrm{C}$$, absorbing $$1500 \ \mathrm{J} of $$heat, what is the heat capacity of the calorimeter?

Accepted Answer

$$C = 98.7 \ \mathrm{J}/^\circ \mathrm{C}$$

Question 9

Which of the following elements is found in its standard state at room temperature and pressure?

Accepted Answer

Cl$$_2 (g)$$

Question 10

Given the reaction $$2 \mathrm{Mg} (s) + \mathrm{O}_2 (g) \rightarrow 2 \mathrm{MgO} (s)$$ with $$\Delta H = -1204 \ \mathrm{kJ}$$, what is the enthalpy change for the formation of 1 mole of MgO?

Accepted Answer

$$-602 \ \mathrm{kJ}$$

Question 11

Which of the following statements about exothermic reactions is correct?

Accepted Answer

Exothermic reactions release heat to the surroundings.

Question 12

A 50.0 g piece of heated metal is placed in an insulated beaker containing 82.5 g of water. Once the metal heats up, the final temperature of the water is $$20.0^\circ \mathrm{C}. If $$the metal gives up $$154.5 \ \mathrm{J} of $$energy, what is the initial temperature of the water? (Specific heat capacity of water = $$4.18 \ \mathrm{J}/\mathrm{g} \cdot ^\circ \mathrm{C})$$

Accepted Answer

$$16.5^\circ \mathrm{C}$$

Question 13

Which of the following best describes thermal equilibrium?

Accepted Answer

When two substances are at the same temperature and no net heat flows between them.

Question 14

Which of the following is the correct formation equation for barium nitrate, Ba(NO$$_3$$)$$_2 (s$$)?

Accepted Answer

$$\mathrm{Ba} (s) + \mathrm{N}_2 (g) + 3 \mathrm{O}_2 (g) \rightarrow \mathrm{Ba(NO}_3)_2 (s)$$

Question 15

A reaction occurs at constant pressure. If the system absorbs 72.4 kJ of heat and the volume compresses from 15.0 L to 5.0 L against a constant pressure of 2.0 atm, what is the change in internal energy ($$\Delta E$$)? ($$1 \mathrm{L} \cdot \mathrm{atm} = 101.3 \ \mathrm{J})$$

Accepted Answer

$$\Delta E = 72.4 \ \mathrm{kJ} + 2.0 	imes (5.0 - 15.0) 	imes 101.3 \ \mathrm{J}$$

Question 16

Which of the following reactions is exothermic?

Accepted Answer

Combustion of methane

Question 17

Given the following reactions:
$$\mathrm{CO} (g) + \frac{1}{2} \mathrm{O}_2 (g) \rightarrow \mathrm{CO}_2 (g) \quad \Delta H = -283.0 \ \mathrm{kJ}$$
$$\mathrm{H}_2 (g) + \frac{1}{2} \mathrm{O}_2 (g) \rightarrow \mathrm{H}_2 \mathrm{O} (l) \quad \Delta H = -286.0 \ \mathrm{kJ}$$
Calculate $$\Delta H$$ for the reaction:
$$\mathrm{CO} (g) + \mathrm{H}_2 (g) + \mathrm{O}_2 (g) \rightarrow \mathrm{CO}_2 (g) + \mathrm{H}_2 \mathrm{O} (l)$$

Accepted Answer

$$\Delta H = -569.0 \ \mathrm{kJ}$$

Question 18

Which of the following is NOT in its standard state at room temperature and pressure?

Accepted Answer

H$$_2O (l)$$

Thermochemistry: Study Notes for General Chemistry

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