Q: Which compound has the larger lattice energy: $$\text{Al}_2\text{O}_3 or$$ $$\text{Al}_2\text{Se}_3$$? Explain your reasoning.

$$\text{Al}_2\text{O}_3$$, because O$$^{2-}$$ has a smaller radius than Se$$^{2-}$$

Q: Which equation correctly represents the enthalpy of formation for ethanol, $$\text{C}_2\text{H}_5\text{OH}(l)$$?

$$2\text{C}(s) + 3\text{H}_2(g) + \frac{1}{2}\text{O}_2(g) \rightarrow \text{C}_2\text{H}_5\text{OH}(l)$$

Q: Which equation is used to calculate the enthalpy change for a reaction using enthalpy of formation values? A. $$\Delta H_{rxn} = \Sigma n \Delta H_f^\circ (\text{products}) - \Sigma n \Delta H_f^\circ (\text{reactants}) B$$. $$\Delta H_{rxn} = \Sigma n \Delta H_f^\circ (\text{reactants}) - \Sigma n \Delta H_f^\circ (\text{products}) C$$. $$\Delta H_{rxn} = \Sigma n \Delta H_f^\circ (\text{products}) + \Sigma n \Delta H_f^\circ (\text{reactants}) D$$. $$\Delta H_{rxn} = \Sigma n \Delta H_f^\circ (\text{reactants}) \times \Sigma n \Delta H_f^\circ (\text{products})$$

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

Question 1

Calculate the amount of heat required to heat 725 g of water from 22.1 °C to 110.5 °C. (cwater = 4.184 J/g°C)

$$ q = mc\Delta T $$

Accepted Answer

268.2 kJ

Question 2

A 38.6 g piece of metal at 75.4°C is dropped into 98.6 g of water originally at 29.5°C. The final temperature of both the metal and water is 37.8°C. What is the specific heat, $$c$$, of the metal? (cwater = 4.184 J/g°C)

$$ q_{metal} = -q_{water} $$

Accepted Answer

2.4 J/g°C

Question 3

What is the change in internal energy for a system that releases 71 J of heat and does $$3.1 	imes 10$$^{-2}$$ kJ of work on its surroundings?

$$ \Delta U = q + w $$

Accepted Answer

-102 J

Question 4

What mass of iron must be in a hot pack to provide -335 kJ of heat when the iron reacts with oxygen and is converted to iron(III) oxide according to the following thermochemical equation?

$$ 2 	ext{Fe}(s) + 1.5 	ext{O}_2(g) ightarrow 	ext{Fe}_2	ext{O}_3(s) \, \Delta H^\circ = -824.2 \, 	ext{kJ} $$

Accepted Answer

45.4 g

Question 5

Using the provided $$\Delta H_f^\circ$$ values, calculate the $$\Delta H_{rxn}^\circ$$ for the following reaction:

$$ 	ext{C}_6	ext{H}_6(l) + 7.5	ext{O}_2(g) ightarrow 6	ext{CO}_2(g) + 3	ext{H}_2	ext{O}(l) $$

Accepted Answer

-3,267.5 kJ

Question 6

Given the information in the provided table, what is $$\Delta H$$ for $$	ext{NO}(g) + 	ext{O}(g) ightarrow 	ext{NO}_2(g)$$?

Accepted Answer

-551.6 kJ

Question 7

Calculate the bond energy of the O-F bond using the standard enthalpy of reaction and the bond energy data provided.

$$ 	ext{OF}_2(g) + 	ext{H}_2	ext{O}(g) ightarrow 	ext{O}_2(g) + 2	ext{HF}(g) \, \Delta H^\circ = -318 \, 	ext{kJ} $$

Accepted Answer

188 kJ

Question 8

Calculate the energy change for the reaction $$	ext{K}(g) + 	ext{Br}(g) ightarrow 	ext{K}^+(g) + 	ext{Br}^-(g)$$ given the ionization energy (IE) and electron affinity (EA) values in the table.

Accepted Answer

95 kJ/mol

Question 9

Which process is exothermic based on the diagram showing heat and work transfer in a system?

(a) $$q  0$$, $$w \u003e 0$$

Accepted Answer

Process (a) is exothermic

Question 10

A calorimeter contains 775 g of water and has a heat capacity of 893 J/°C. If the temperature increases from 23.8 °C to 35.6 °C, what is the total heat absorbed by the calorimeter and water?

$$ q_{total} = q_{water} + q_{calorimeter} $$

Accepted Answer

48,800 J

Question 11

Which compound has the larger lattice energy: $$	ext{Al}_2	ext{O}_3 or$$ $$	ext{Al}_2	ext{Se}_3$$? Explain your reasoning.

Accepted Answer

$$	ext{Al}_2	ext{O}_3$$, because O$$^{2-}$$ has a smaller radius than Se$$^{2-}$$

Question 12

Which of the following is a state function?

A. Heat ($$q)
B. $$Work ($$w)
C. $$Enthalpy ($$H)
D. $$Path taken by the system

Accepted Answer

Enthalpy ($$H)$$

Question 13

Which equation correctly represents the enthalpy of formation for ethanol, $$	ext{C}_2	ext{H}_5	ext{OH}(l)$$?

Accepted Answer

$$2	ext{C}(s) + 3	ext{H}_2(g) + \frac{1}{2}	ext{O}_2(g) ightarrow 	ext{C}_2	ext{H}_5	ext{OH}(l)$$

Question 14

Which of the following statements about bond energies is correct?

Accepted Answer

Breaking bonds is always endothermic

Question 15

According to Hess's Law, what happens to $$\Delta H if $$you reverse a chemical equation?

Accepted Answer

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

Question 16

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

A. $$\Delta H_{rxn} = \Sigma n \Delta H_f^\circ (	ext{products}) - \Sigma n \Delta H_f^\circ (	ext{reactants})
B$$. $$\Delta H_{rxn} = \Sigma n \Delta H_f^\circ (	ext{reactants}) - \Sigma n \Delta H_f^\circ (	ext{products})
C$$. $$\Delta H_{rxn} = \Sigma n \Delta H_f^\circ (	ext{products}) + \Sigma n \Delta H_f^\circ (	ext{reactants})
D$$. $$\Delta H_{rxn} = \Sigma n \Delta H_f^\circ (	ext{reactants}) 	imes \Sigma n \Delta H_f^\circ (	ext{products})$$

Accepted Answer

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

Thermochemistry and Calorimetry: Step-by-Step Study Guidance

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