General Chemistry Exam 3 Review – Step-by-Step Study Guidance

Q1. If 10 g of sodium bicarbonate (NaHCO3) is combined with an excess of hydrochloric acid (HCl), how many L of carbon dioxide (CO2) gas are produced, if the pressure is 1.0 atm and the temperature is 20 °C?

Background

Topic: Stoichiometry and Gas Laws

This question tests your ability to use stoichiometry to determine the amount of gas produced in a chemical reaction and then apply the ideal gas law to find the volume of gas at given conditions.

Key Terms and Formulas

• Mole-to-mole relationships from balanced chemical equations

• Molar mass: NaHCO3 = 84.01 g/mol

• Ideal Gas Law: $PV = nRT$

• R (gas constant): $0.0821\ \mathrm{L\cdot atm\cdot mol^{-1}\cdot K^{-1}}$

• Temperature must be in Kelvin: $T(\mathrm{K}) = T(\degree C) + 273.15$

Step-by-Step Guidance

1. Write the balanced chemical equation for the reaction between NaHCO3 and HCl. Identify the stoichiometry for CO2 production.

2. Calculate the number of moles of NaHCO3 used: $n = \frac{\text{mass}}{\text{molar mass}}$.

3. Use the stoichiometry from the balanced equation to determine the moles of CO2 produced.

4. Convert the temperature to Kelvin: $T = 20 + 273.15$.

5. Set up the ideal gas law to solve for the volume of CO2: $V = \frac{nRT}{P}$, but do not calculate the final value yet.

Try solving on your own before revealing the answer!

Q2. What are the three principles of kinetic molecular theory?

Background

Topic: Kinetic Molecular Theory of Gases

This question tests your understanding of the foundational assumptions that explain the behavior of ideal gases.

Key Terms

• Kinetic molecular theory

• Assumptions about gas particles

Step-by-Step Guidance

1. Recall that the kinetic molecular theory describes the motion and interactions of gas particles.

2. List the three main postulates (think about particle size, motion, and interactions).

3. For each principle, briefly explain what it means in terms of gas behavior.

Try summarizing the three principles before checking the answer!

Q3. What is pressure?

Background

Topic: Gas Properties

This question asks you to define pressure in the context of gases and understand its physical meaning.

Key Terms

• Pressure ($P$)

• Force, area

• Units: atm, Pa, torr, mmHg

Step-by-Step Guidance

1. Recall the definition of pressure as force per unit area.

2. Write the formula: $P = \frac{F}{A}$, where $F$ is force and $A$ is area.

3. Think about how this applies to gas particles colliding with the walls of a container.

Try writing your own definition before revealing the answer!

Q4. Rationalize Boyle’s Law, Charles’s Law, Avogadro’s Law, and Dalton’s Law according to kinetic molecular theory.

Background

Topic: Gas Laws and Kinetic Molecular Theory

This question tests your ability to connect the macroscopic gas laws to the microscopic behavior of gas particles as described by kinetic molecular theory.

Key Terms

• Boyle’s Law: $P \propto \frac{1}{V}$ (at constant $T$ and $n$)

• Charles’s Law: $V \propto T$ (at constant $P$ and $n$)

• Avogadro’s Law: $V \propto n$ (at constant $P$ and $T$)

• Dalton’s Law: $P_{\text{total}} = \sum P_i$

Step-by-Step Guidance

1. For each law, recall what the law states about the relationship between variables.

2. Think about how the kinetic molecular theory explains each relationship (e.g., what happens to particle collisions when volume or temperature changes).

3. Write a brief explanation for each law, connecting the macroscopic observation to particle behavior.

Try explaining each law in your own words before checking the answer!

Q5. If NH3 and HCl are each released into still air, how far will the NH3 have effused when the HCl has diffused 1.00 meter?

Background

Topic: Diffusion and Effusion of Gases

This question tests your understanding of Graham’s Law, which relates the rates of effusion (or diffusion) of gases to their molar masses.

Key Terms and Formulas

• Graham’s Law: $\frac{\text{rate}_1}{\text{rate}_2} = \sqrt{\frac{M_2}{M_1}}$

• Effusion and diffusion

• Molar masses: NH3 = 17.03 g/mol, HCl = 36.46 g/mol

Step-by-Step Guidance

1. Write Graham’s Law for the rates of NH3 and HCl.

2. Set up the ratio: $\frac{\text{distance}_{NH_3}}{\text{distance}_{HCl}} = \sqrt{\frac{M_{HCl}}{M_{NH_3}}}$.

3. Plug in the molar masses for NH3 and HCl.

4. Since HCl has diffused 1.00 meter, set $\text{distance}_{HCl} = 1.00$ m and solve for $\text{distance}_{NH_3}$, but do not calculate the final value yet.

Try setting up the calculation before revealing the answer!

Q6. Explain the conditions where the assumptions of the gas laws fail. What formula describes the behavior of gases under these unique conditions?

Background

Topic: Real Gases and Deviations from Ideal Behavior

This question tests your understanding of when and why real gases deviate from ideal gas behavior, and what equation is used to describe real gases.

Key Terms and Formulas

• Ideal gas assumptions

• High pressure, low temperature

• Van der Waals equation: $\left(P + a\frac{n^2}{V^2}\right)(V - nb) = nRT$

Step-by-Step Guidance

1. List the main assumptions of the ideal gas law (e.g., negligible volume, no intermolecular forces).

2. Describe the conditions (high pressure, low temperature) where these assumptions break down.

3. Name and write the equation that accounts for real gas behavior (Van der Waals equation).

Try explaining the deviations and writing the formula before checking the answer!