Q: Which of the following equations correctly represents the relationship for calculating the heat absorbed or released by a substance?

$$q = m \times C_s \times \Delta T$$

Question 1

Which of the following statements best describes an exothermic reaction?

Accepted Answer

A reaction that produces heat, resulting in an increase in the temperature of the surroundings.

Question 2

Given the reaction $$\mathrm{CH_4$(g) + 2\ O_2$(g) \rightarrow CO_2$(g) + 2\ H_2O(l)}$$ with $$\Delta H = -890\ \mathrm{kJ}$$, what is the enthalpy change for the reverse reaction?

Accepted Answer

$$\Delta H = +890\ \mathrm{kJ}$$

Question 3

A 35.2 g sample of iron increases in temperature from $$23.7^\circ \mathrm{C} to$$ $$29.5^\circ \mathrm{C}. If $$the specific heat of iron is $$0.450\ \mathrm{J/g\cdot K}$$, how many joules of heat are absorbed?

Accepted Answer

$$92\ \mathrm{J}$$

Question 4

Which of the following substances has the highest specific heat capacity at $$298\ \mathrm{K}$$?

Accepted Answer

$$\mathrm{H_2O(l)}$$

Question 5

Which calorimeter is best suited for measuring the heat of combustion of a fuel?

Accepted Answer

Bomb calorimeter

Question 6

Calculate the enthalpy change for the combustion of 1 mol of ethanol using the following data:
$$\mathrm{C_2H_5OH(l) + 3\ O_2$(g) \rightarrow 2\ CO_2$(g) + 3\ H_2O(l)}$$
$$\Delta H_f^\circ (\mathrm{C_2H_5OH(l)}) = -277.7\ \mathrm{kJ/mol}$$
$$\Delta H_f^\circ (\mathrm{CO_2$(g)}) = -393.5\ \mathrm{kJ/mol}$$
$$\Delta H_f^\circ (\mathrm{H_2O(l)}) = -285.8\ \mathrm{kJ/mol}$$

Accepted Answer

$$-1367\ \mathrm{kJ}$$

Question 7

Which of the following has a standard enthalpy of formation ($$\Delta H_f^\circ) of $$zero?

Accepted Answer

$$\mathrm{C(graphite)}$$

Question 8

For which of the following reactions is $$\Delta H_{rxn}^\circ$$ equal to the standard enthalpy of formation ($$\Delta H_f^\circ) $$for the product?

Accepted Answer

$$\mathrm{Xe(g) + 2\ F_2$(g) \rightarrow $$XeF_4$$(g)}$$

Question 9

Using Hess's Law and the following data, calculate $$\Delta H$$ for the reaction $$\mathrm{C(s) + \frac{1}{2}O_2$(g) \rightarrow CO(g)}$$:
(1) $$\mathrm{C(s) + O_2$(g) \rightarrow CO_2$(g)}$$, $$\Delta H = -393.5\ \mathrm{kJ}
(2$$) $$\mathrm{CO(g) + \frac{1}{2}O_2$(g) \rightarrow CO_2$(g)}$$, $$\Delta H = -283.0\ \mathrm{kJ}$$

Accepted Answer

$$-110.5\ \mathrm{kJ}$$

Question 10

Which of the following best describes the process measured by a coffee-cup calorimeter?

Accepted Answer

Constant pressure process

Question 11

A reaction in a bomb calorimeter releases 5000 J of heat. What is the sign of $$\Delta H$$ and what does it indicate?

Accepted Answer

$$\Delta H is $$negative; the reaction is exothermic.

Question 12

Which of the following equations correctly represents the relationship for calculating the heat absorbed or released by a substance?

Accepted Answer

$$q = m 	imes C_s 	imes \Delta T$$

Question 13

Which of the following is a correct statement about the standard enthalpy of formation ($$\Delta H_f^\circ$$)?

Accepted Answer

It is the enthalpy change when 1 mole of a compound is formed from its elements in their standard states.

Question 14

Given the following data:
$$\mathrm{C_2H_2(g) + \frac{5}{2}O_2$(g) \rightarrow 2CO_2(g) + H_2O(l)}$$, $$\Delta H = -1299.6\ \mathrm{kJ}$$
$$\mathrm{C(s) + O_2$(g) \rightarrow CO_2$(g)}$$, $$\Delta H = -393.5\ \mathrm{kJ}$$
$$\mathrm{H_2$(g) + \frac{1}{2}O_2$(g) \rightarrow H_2O(l)}$$, $$\Delta H = -285.8\ \mathrm{kJ}$$
Calculate $$\Delta H$$ for $$\mathrm{2C(s) + H_2$(g) \rightarrow C_2H_2(g)}.$$

Accepted Answer

$$+226.7\ \mathrm{kJ}$$

Question 15

Which of the following reactions is endothermic?

Accepted Answer

$$\Delta H = +890\ \mathrm{kJ}$$

Question 16

If 4.5 g of methane ($$\mathrm{CH_4$}) is $$burned in excess oxygen, how much heat is released? ($$\Delta H = -890\ \mathrm{kJ}$$ for $$\mathrm{CH_4$(g) + 2O_2(g) \rightarrow CO_2$(g) + 2H_2O(l)}$$; molar mass of $$\mathrm{CH_4$} = 16.0 g/$$mol)

Accepted Answer

$$-250\ \mathrm{kJ}$$

Question 17

Which of the following is NOT a correct statement about specific heat capacity?

Accepted Answer

It is the same for all substances.

Question 18

Which of the following would have $$\Delta H_f^\circ = 0 at$$ $$298\ \mathrm{K}$$?

Accepted Answer

$$\mathrm{O_2$(g)}$$

Question 19

Which of the following best explains why the enthalpy of formation of $$\mathrm{C(graphite)} is $$zero, but that of $$\mathrm{C(diamond)} is $$not?

Accepted Answer

$$\mathrm{C(graphite)} is $$the most stable form of carbon at standard conditions.

Thermochemistry: Enthalpy, Calorimetry, and Enthalpies of Formation

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