General Chemistry II Practice Final Exam – Step-by-Step Study Guidance

Q1. Which of the following equalities shows an incorrect relationship between pressures given in different units?

Background

Topic: Gas Laws and Pressure Units

This question tests your understanding of how to convert between different units of pressure, such as atm, torr, mm Hg, kPa, and bar.

Key Terms and Formulas:

• 1 atm = 760 torr = 760 mm Hg = 101.325 kPa = 1.01325 bar

• Conversion factors are essential for comparing values in different units.

Step-by-Step Guidance

1. Review the standard pressure conversions listed above.

2. For each option, convert one unit to the other using the conversion factors.

3. Check if the equality is correct by performing the calculation for at least two options.

4. Identify which option does not match the correct conversion.

Try solving on your own before revealing the answer!

Q2. According to kinetic molecular theory, in which of the following gases will the root-mean-square velocity of the molecules be the highest at 150 °C?

Background

Topic: Kinetic Molecular Theory and Molecular Speeds

This question tests your understanding of how molecular mass and temperature affect the root-mean-square (rms) velocity of gas molecules.

Key Terms and Formulas:

• Root-mean-square velocity ($u_{rms}$): $u_{rms} = \sqrt{\frac{3RT}{M}}$

• R = 8.314 J/(mol·K)

• T = temperature in Kelvin

• M = molar mass in kg/mol

Step-by-Step Guidance

1. Convert 150 °C to Kelvin: $T = 150 + 273 = 423$ K.

2. List the molar masses of each gas (in kg/mol).

3. Recall that $u_{rms}$ is inversely proportional to the square root of molar mass.

4. Identify which gas has the lowest molar mass, as it will have the highest $u_{rms}$.

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Q3. What is the density (g/L) of BrCl gas in a 5.00-L tank at 1.2 atm and 35 °C?

Background

Topic: Gas Density and Ideal Gas Law

This question tests your ability to use the ideal gas law to calculate the density of a gas under non-standard conditions.

Key Terms and Formulas:

• Density formula: $d = \frac{MP}{RT}$

• M = molar mass of BrCl (g/mol)

• P = pressure (atm)

• R = 0.08206 L·atm/(mol·K)

• T = temperature in Kelvin

Step-by-Step Guidance

1. Convert 35 °C to Kelvin: $T = 35 + 273 = 308$ K.

2. Calculate the molar mass of BrCl (Br = 79.90 g/mol, Cl = 35.45 g/mol).

3. Plug the values for M, P, R, and T into the density formula.

4. Set up the calculation for $d = \frac{MP}{RT}$, but do not compute the final value yet.

Try solving on your own before revealing the answer!

Q4. A sample of gas is placed into a 2.0-L balloon at 25 °C and 1.5 atm. The balloon is heated to 40 °C and pressurized to 0.50 atm. What is the final volume (L) of the gas?

Background

Topic: Combined Gas Law

This question tests your ability to use the combined gas law to relate pressure, volume, and temperature changes for a fixed amount of gas.

Key Terms and Formulas:

• Combined Gas Law: $\frac{P_1 V_1}{T_1} = \frac{P_2 V_2}{T_2}$

• Temperatures must be in Kelvin.

Step-by-Step Guidance

1. Convert all temperatures to Kelvin: $T_1 = 25 + 273 = 298$ K, $T_2 = 40 + 273 = 313$ K.

2. List the known values: $P_1 = 1.5$ atm, $V_1 = 2.0$ L, $T_1 = 298$ K, $P_2 = 0.50$ atm, $T_2 = 313$ K.

3. Plug these values into the combined gas law and rearrange to solve for $V_2$.

4. Set up the equation for $V_2$, but do not solve for the final value yet.

Try solving on your own before revealing the answer!

Q5. What mass (g) of hydrogen gas is contained in a 10.0-L vessel at 25 °C and 1.0 atm?

Background

Topic: Ideal Gas Law and Moles-to-Mass Conversion

This question tests your ability to use the ideal gas law to find the number of moles of a gas, then convert to mass using molar mass.

Key Terms and Formulas:

• Ideal Gas Law: $PV = nRT$

• Moles to mass: $\text{mass} = n \times M$

• Molar mass of H2 = 2.02 g/mol

• R = 0.08206 L·atm/(mol·K)

Step-by-Step Guidance

1. Convert 25 °C to Kelvin: $T = 25 + 273 = 298$ K.

2. List the known values: $P = 1.0$ atm, $V = 10.0$ L, $R = 0.08206$, $T = 298$ K.

3. Rearrange the ideal gas law to solve for $n$: $n = \frac{PV}{RT}$.

4. Set up the calculation for $n$, then multiply by the molar mass to get the mass of H2.

Try solving on your own before revealing the answer!