Q: A researcher measures the pH of a solution and finds it to be 5. What is the pOH of this solution?

$$\text{pOH} = 9$$, because $$\text{pH} + \text{pOH} = 14$$

Q: A buffer solution is made by mixing acetic acid and sodium acetate. If the concentration of acetate ions $$[A^-] is $$increased, what happens to the pH of the solution according to the Henderson-Hasselbalch equation?

The pH increases because $$\text{pH} = pK_a + \log \frac{[A^-]}{[HA]}.$$

Q: A gas sample is collected in a 2.0 L container at 300 K and 1.0 atm. Using the ideal gas law, how many moles of gas are present? ($$R = 0.0821\ L \cdot atm \cdot $$mol^{-1}$$ \cdot K$$^{-1}$$)

$$n = \frac{PV}{RT} = \frac{1.0 \times 2.0}{0.0821 \times 300} \approx 0.081$$ moles

Q: A patient is experiencing acidosis, and their blood pH is measured at 7.1. What is the corresponding pOH?

$$\text{pOH} = 6.9$$, because $$\text{pH} + \text{pOH} = 14$$

Question 1

A biologist is studying the rate of a first-order reaction in a metabolic pathway. If the initial concentration of the reactant is doubled, what will happen to the rate of the reaction, assuming all other conditions remain constant?

Accepted Answer

The rate will double because for first-order reactions, rate is directly proportional to reactant concentration: $$	ext{rate} = k[A].$$

Question 2

A researcher measures the pH of a solution and finds it to be 5. What is the pOH of this solution?

Accepted Answer

$$	ext{pOH} = 9$$, because $$	ext{pH} + 	ext{pOH} = 14$$

Question 3

Which equation would you use to calculate the equilibrium constant $$K_p$$ for a gaseous reaction at a given temperature?

Accepted Answer

$$K_p = K_c (RT$$)^{\Delta n}$$

Question 4

A cell is using an electrochemical gradient to drive the synthesis of ATP. If the cell's membrane potential is increased, what effect does this have on the Gibbs free energy change ($$\Delta G) $$for ATP synthesis?

Accepted Answer

$$\Delta G$$ becomes more positive, making ATP synthesis less favorable.

Question 5

A scientist is studying the effect of temperature on the rate constant $$k of an $$enzyme-catalyzed reaction. Which equation should they use to determine how $$k$$ changes with temperature?

Accepted Answer

$$\ln k = -\frac{E_a}{RT} + \ln A$$

Question 6

A buffer solution is made by mixing acetic acid and sodium acetate. If the concentration of acetate ions $$[A^-] is $$increased, what happens to the pH of the solution according to the Henderson-Hasselbalch equation?

Accepted Answer

The pH increases because $$	ext{pH} = pK_a + \log \frac{[A^-]}{[HA]}.$$

Question 7

A gas sample is collected in a 2.0 L container at 300 K and 1.0 atm. Using the ideal gas law, how many moles of gas are present? ($$R = 0.0821\ L \cdot atm \cdot $$mol^{-1}$$ \cdot K$$^{-1}$$)

Accepted Answer

$$n = \frac{PV}{RT} = \frac{1.0 	imes 2.0}{0.0821 	imes 300} \approx 0.081$$ moles

Question 8

During a laboratory experiment, a student calculates the standard cell potential ($$E_{cell}) $$for a redox reaction at 25°C. Which equation should they use if they know the concentrations of the reactants and products?

Accepted Answer

$$E_{cell} = E_{cell}^\circ - \frac{0.0592}{n} \log Q$$

Question 9

A reaction has an enthalpy change $$\Delta H^\circ = -100 kJ/$$mol and an entropy change $$\Delta S^\circ = -200 J/($$mol·K). At what temperature will the reaction become non-spontaneous? (Recall $$\Delta G^\circ = \Delta H^\circ - T \Delta S^\circ)$$

Accepted Answer

$$T \u003e 500 K$$, because $$\Delta G^\circ$$ becomes positive when $$T \u003e \frac{\Delta H^\circ}{\Delta S^\circ}$$

Question 10

A patient is experiencing acidosis, and their blood pH is measured at 7.1. What is the corresponding pOH?

Accepted Answer

$$	ext{pOH} = 6.9$$, because $$	ext{pH} + 	ext{pOH} = 14$$

Question 11

A chemical reaction is at equilibrium. Which of the following statements is true regarding the concentrations of reactants and products?

Accepted Answer

The concentrations of reactants and products remain constant over time.

Question 12

A scientist is comparing two reactions with different activation energies ($$E_a). $$According to the Arrhenius equation, which reaction will have a higher rate constant $$k at $$the same temperature?

Accepted Answer

The reaction with the lower $$E_a$$ will have a higher $$k$$, because $$k = Ae$$^{-E_a/RT}$$.

Question 13

A biologist is studying a gas exchange process in the lungs. If the partial pressure of oxygen in the alveoli ($$P_A) is 100 $$mmHg and in the blood ($$P_a) is 40 $$mmHg, what is the direction of oxygen diffusion?

Accepted Answer

Oxygen will diffuse from the alveoli to the blood, moving from high to low partial pressure.

Question 14

A solution contains 0.01 M HCl. What is the pH of the solution?

Accepted Answer

$$	ext{pH} = 2$$, because $$	ext{pH} = -\log[H^+]$$

Question 15

A researcher is analyzing the effect of pressure on the solubility of a gas in a liquid. Which law and equation should they use?

Accepted Answer

Henry's Law: $$S_g = k_H P_g$$

Question 16

A student is asked to calculate the change in entropy ($$\Delta S) $$for a reaction. Which of the following is the correct unit for entropy in the context of thermodynamics?

Accepted Answer

$$J \cdot $$mol^{-1}$$ \cdot K$$^{-1}$$

Question 17

A chemical reaction has $$\Delta G^\circ \u003c 0. $$What does this indicate about the spontaneity of the reaction under standard conditions?

Accepted Answer

The reaction is spontaneous.

Question 18

A scientist is using the quadratic formula to solve for the concentration of a reactant in a chemical equilibrium problem. Which is the correct form of the quadratic formula?

Accepted Answer

$$x = \frac{-b \pm \sqrt{b^2$ - 4ac}}{2a}$$

Key Equations and Concepts in General Chemistry and Thermodynamics

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