Q: A student writes the following thermochemical equation: $$\text{CH}_4(g) + 2\text{O}_2(g) \rightarrow \text{CO}_2(g) + 2\text{H}_2\text{O}(l)\ \Delta H = -890\ \text{kJ/mol}. $$What does the $$\Delta H$$ value represent?

The enthalpy change for the reaction of 1 mol of $$\text{CH}_4$$ under standard conditions.

Q: Which of the following is NOT a correct use of SI prefixes?

2.718 m for $$2.718 \times 10$$^{-3}$$ m

Question 1

Which of the following best describes an exothermic reaction?

Accepted Answer

A reaction in which heat is released to the surroundings, resulting in a negative $$\Delta H.$$

Question 2

Given the reaction: $$2	ext{Na}(s) + 2	ext{H}_2	ext{O}(l) ightarrow 2	ext{NaOH}(aq) + 	ext{H}_2(g)$$ with $$\Delta H = -368.6\ 	ext{kJ}$$, what does the negative sign of $$\Delta H$$ indicate?

Accepted Answer

The reaction is exothermic and releases heat.

Question 3

Which equation correctly relates enthalpy change ($$\Delta H) to $$internal energy change ($$\Delta U) $$and pressure-volume work at constant pressure?

Accepted Answer

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

Question 4

In bomb calorimetry, which of the following is true regarding the measurement of heat?

Accepted Answer

The reaction occurs at constant volume and measures $$q_v.$$

Question 5

Which property of enthalpy ($$H) $$makes it useful for determining the heat absorbed or evolved in a chemical reaction at constant pressure?

Accepted Answer

It is a state function and extensive property.

Question 6

A student writes the following thermochemical equation: $$	ext{CH}_4(g) + 2	ext{O}_2(g) ightarrow 	ext{CO}_2(g) + 2	ext{H}_2	ext{O}(l)\ \Delta H = -890\ 	ext{kJ/mol}. $$What does the $$\Delta H$$ value represent?

Accepted Answer

The enthalpy change for the reaction of 1 mol of $$	ext{CH}_4$$ under standard conditions.

Question 7

Which of the following best explains why scientific notation is used in chemistry?

Accepted Answer

To express very large or very small numbers in a concise and manageable format.

Question 8

If a reaction occurs at constant pressure and the volume increases, which term accounts for the work done by the system?

Accepted Answer

$$P\Delta V$$

Question 9

Which of the following is the correct definition of standard enthalpy change ($$\Delta H^\circ$$)?

Accepted Answer

The enthalpy change for a reaction with pure reactants and products at 1 bar pressure and 25°C.

Question 10

Which SI prefix corresponds to $$10^{-9}$$?

Accepted Answer

Nano

Question 11

A chemical reaction has $$\Delta H = +120\ 	ext{kJ}. $$Which statement is true?

Accepted Answer

The reaction is endothermic and absorbs 120 kJ of heat.

Question 12

Which of the following is NOT a correct use of SI prefixes?

Accepted Answer

2.718 m for $$2.718 	imes 10$$^{-3}$$ m

Question 13

Which equation would you use to calculate the enthalpy change for a reaction at constant pressure?

Accepted Answer

$$\Delta H = H_{	ext{products}} - H_{	ext{reactants}}$$

Question 14

A student is measuring the heat of a reaction in a coffee cup calorimeter. Which condition is being held constant?

Accepted Answer

Pressure

Question 15

Which of the following statements about bond breaking and bond making is correct?

Accepted Answer

Bond breaking requires energy and bond making releases energy.

Question 16

If $$\Delta H_{	ext{run}} = \sum H_{	ext{products}} - \sum H_{	ext{reactants}}$$, what does this equation calculate?

Accepted Answer

The enthalpy change for the reaction based on stoichiometric amounts.

Question 17

Which of the following is an example of a quantity expressed in scientific notation?

Accepted Answer

3.14165 	imes $$10^4$$

Question 18

A reaction is performed in a bomb calorimeter and the measured heat is $$q_v. $$How is the change in internal energy ($$\Delta U) $$related to $$q_v$$?

Accepted Answer

$$\Delta U = q_v$$

Question 19

Which of the following best describes an extensive property?

Accepted Answer

A property that depends on the amount of substance present.

Thermochemistry: Enthalpy, Heat of Reaction, and Scientific Quantities

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