Question 1

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

Accepted Answer

Energy cannot be created or destroyed, only transferred or transformed.

Question 2

A chemical reaction in a laboratory releases 250 J of heat to the surroundings and does 150 J of work on the surroundings. What is the change in internal energy ($$\Delta E) of $$the system?

Accepted Answer

$$\Delta E = -400\ \mathrm{J}$$

Question 3

Which of the following best defines enthalpy ($$H$$)?

Accepted Answer

The sum of the internal energy and the product of pressure and volume: $$H = E + PV.$$

Question 4

A student mixes 50.0 mL of 1.0 M HCl with 50.0 mL of 1.0 M NaOH in a coffee-cup calorimeter. The temperature rises from 22.0$$^\circC to 28.0$^\circC. $$Assuming the solution has the same density and specific heat as water ($$4.18\ \mathrm{J/g\cdot K}$$), what is the heat ($$q) $$released by the reaction? (Assume total mass is 100 g.)

Accepted Answer

$$q = 2,508\ \mathrm{J}$$

Question 5

Which of the following is true about an exothermic reaction?

Accepted Answer

The enthalpy change ($$\Delta H) is $$negative.

Question 6

Given the following reactions:

$$\mathrm{C(s) + O_2$(g) \rightarrow CO_2$(g)}\ \Delta H = -393.5\ \mathrm{kJ}$$

$$\mathrm{CO_2$(g) + H_2O(l) \rightarrow H_2CO_3(aq)}\ \Delta H = -45.0\ \mathrm{kJ}$$

What is the enthalpy change for the reaction $$\mathrm{C(s) + O_2$(g) + H_2O(l) \rightarrow H_2CO_3(aq)}$$?

Accepted Answer

$$\Delta H = -438.5\ \mathrm{kJ}$$

Question 7

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

Accepted Answer

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

Question 8

A reaction has an activation energy of $$75\ \mathrm{kJ/mol}. If a $$catalyst lowers the activation energy to $$40\ \mathrm{kJ/mol}$$, what is the effect on the rate of the reaction?

Accepted Answer

The rate increases because more molecules have enough energy to react.

Question 9

Which of the following factors does NOT affect the rate of a chemical reaction?

Accepted Answer

The color of the reactants

Question 10

For the reaction $$\mathrm{2NO_2(g) \rightarrow 2NO(g) + O_2$(g)}$$, the rate law is $$\mathrm{rate = k[NO_2$]^2}. If $$the concentration of $$\mathrm{NO_2$} is $$doubled, how does the rate change?

Accepted Answer

The rate increases by a factor of four.

Question 11

A reaction is first order in $$\mathrm{A}$$ and zero order in $$\mathrm{B}. $$Which of the following is the correct rate law?

Accepted Answer

$$\mathrm{rate = k[A]}$$

Question 12

The half-life for a first-order reaction is given by which of the following equations?

Accepted Answer

$$t_{1/2} = \dfrac{0.693}{k}$$

Question 13

Which of the following best explains why increasing temperature generally increases the rate of a chemical reaction?

Accepted Answer

It increases the frequency and energy of molecular collisions.

Question 14

Consider the following mechanism for a reaction:

Step 1: $$\mathrm{A + B \rightarrow C} ($$slow)

Step 2: $$\mathrm{C + D \rightarrow E} ($$fast)

Which step determines the overall rate law?

Accepted Answer

Step 1, because it is the slow (rate-determining) step.

Question 15

A reaction has a rate constant $$k$$ that increases from $$1.2 	imes 10$$^{-3}$$\ \mathrm{s}^{-1} to$$ $$4.8 	imes 10$$^{-3}$$\ \mathrm{s}^{-1}$$ when the temperature is raised from $$300\ \mathrm{K} to$$ $$320\ \mathrm{K}. $$Which equation relates the rate constant to temperature?

Accepted Answer

$$k = Ae$$^{-E_a/RT}$$

Question 16

Which of the following is a correct statement about catalysts?

Accepted Answer

Catalysts provide an alternative pathway with a lower activation energy.

Question 17

A real-world example: In the catalytic converter of a car, platinum acts as a catalyst for the reaction $$\mathrm{2CO + O_2$ \rightarrow 2CO_2}. $$What is the main role of platinum in this process?

Accepted Answer

It provides a surface for the reaction to occur more rapidly.

Question 18

Which of the following best describes the relationship between enthalpy and internal energy for a chemical reaction at constant pressure?

Accepted Answer

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

Question 19

A student is studying the decomposition of hydrogen peroxide: $$\mathrm{2H_2O_2(aq) \rightarrow 2H_2O(l) + O_2$(g)}. If $$the rate law is $$\mathrm{rate = k[H_2O_2]}$$, what is the order of the reaction with respect to $$\mathrm{H_2O_2}$$?

Accepted Answer

First order

Thermochemistry and Chemical Kinetics: Study Notes

Guida di studio - Domande di pratica

Study guide - Flashcard