Q: Which formula is used to calculate the heat absorbed or released by a solution in a calorimeter?

$$q_{\text{solution}} = m \times C_{s} \times \Delta T$$

Question 1

Which of the following statements best describes the enthalpy change ($$\Delta H) $$for a chemical reaction occurring at constant pressure?

Accepted Answer

$$\Delta H is $$the amount of heat absorbed or released by the system at constant pressure.

Question 2

A student burns propane ($$\mathrm{C_3H_8}) in a $$coffee-cup calorimeter at constant pressure. Which equation correctly relates the heat evolved ($$q_{p}) to $$the enthalpy change ($$\Delta H) $$for this reaction?

Accepted Answer

$$q_{p} = \Delta H$$

Question 3

Which of the following processes is endothermic and would have a positive $$\Delta H$$?

Accepted Answer

Sweat evaporating from skin

Question 4

Given the reaction $$\mathrm{C_3H_8(g) + 5O_2(g) \rightarrow 3CO_2(g) + 4H_2O(l)}$$ with $$\Delta H = -2044\ \mathrm{kJ}$$, what does the negative sign of $$\Delta H$$ indicate?

Accepted Answer

The reaction is exothermic and releases heat to the surroundings.

Question 5

Which of the following best describes the difference between $$\Delta H$$ and $$\Delta E$$ for a chemical reaction at constant pressure?

Accepted Answer

$$\Delta H$$ and $$\Delta E$$ are identical when no $$P\Delta V$$ work is done.

Question 6

A coffee-cup calorimeter is used to measure the enthalpy change of a reaction. Which assumption is made about the heat exchange in this setup?

Accepted Answer

The heat gained by the solution equals the heat lost by the reaction.

Question 7

If 1.00 mol of $$\mathrm{C_3H_8}$$ reacts with 5.00 mol of $$\mathrm{O_2$} to $$form 3.00 mol of $$\mathrm{CO_2$}$$ and 4.00 mol of $$\mathrm{H_2O}$$, how much heat is emitted according to the reaction $$\mathrm{C_3H_8(g) + 5O_2(g) \rightarrow 3CO_2(g) + 4H_2O(l)}$$; $$\Delta H = -2044\ \mathrm{kJ}$$?

Accepted Answer

$$-2044\ \mathrm{kJ}$$

Question 8

Which of the following reactions is most likely to feel cold to the touch due to its enthalpy change?

Accepted Answer

An endothermic reaction with a positive $$\Delta H$$

Question 9

A student mixes magnesium metal with hydrochloric acid in a coffee-cup calorimeter. The temperature of the solution increases. What can be concluded about the sign of $$\Delta H$$ for the reaction?

Accepted Answer

$$\Delta H is $$negative because heat is released.

Question 10

Which formula is used to calculate the heat absorbed or released by a solution in a calorimeter?

Accepted Answer

$$q_{	ext{solution}} = m 	imes C_{s} 	imes \Delta T$$

Question 11

Which of the following best describes Hess's Law?

Accepted Answer

The enthalpy change for a reaction is independent of the pathway taken.

Question 12

Consider the following reactions:
$$A + 2B \rightarrow C$$; $$\Delta H_1$
C$$ \rightarrow 2D$$; $$\Delta $$H_2$$
What is the enthalpy change for the overall reaction $$A + 2B \rightarrow 2D$$?

Accepted Answer

$$\Delta H_1$ + \Delta H_2$

Question 13

A solution is prepared by mixing 100.0 g of water (specific heat $$4.18\ \mathrm{J/g$$^{\circ}$$C}) $$and a salt. The temperature increases by $$2.5^{\circ}C$. What is the heat absorbed by the solution?

Accepted Answer

$$1045\ \mathrm{J}$$

Question 14

Which of the following is true about the relationship between $$\Delta H$$ and $$\Delta E$$ for reactions involving gases?

Accepted Answer

$$\Delta H = \Delta E + P\Delta V$$

Question 15

Which of the following is a correct statement about constant-pressure calorimetry?

Accepted Answer

It measures the enthalpy change ($$\Delta H) of a $$reaction.

Question 16

A chemical reaction is carried out in a bomb calorimeter at constant volume. Which thermodynamic quantity is directly measured?

Accepted Answer

Internal energy change ($$\Delta E)$$

Question 17

Which of the following is a real-world example of an exothermic process?

Accepted Answer

Gasoline burning in the cylinder of an automobile engine

Question 18

If the temperature of a solution decreases during a reaction in a calorimeter, what can be inferred about the reaction?

Accepted Answer

The reaction is endothermic and absorbs heat from the solution.

Question 19

Which of the following quantitative relationships allows determination of $$\Delta H_{	ext{rxn}}$$ for a reaction without direct measurement?

Accepted Answer

Hess's Law

Thermochemistry: Enthalpy, Calorimetry, and Stoichiometry in Chemical Reactions

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