Q1. What are the units for the reaction rate?

Background

Topic: Chemical Kinetics

This question tests your understanding of how reaction rates are expressed in terms of concentration and time.

Key Terms and Formulas:

• Reaction rate: The change in concentration of a reactant or product per unit time.

• Common units: mol L-1 s-1 (moles per liter per second)

Step-by-Step Guidance

1. Recall that reaction rate is typically measured as the change in concentration () over time ().

2. Concentration is usually in units of mol/L, and time is in seconds.

3. Combine these units to get the standard unit for reaction rate.

4. Compare the answer choices to see which matches this unit.

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Q2. For the reaction A + 2B → products, the rate law is rate = k[A][B]^2. If [B] increases from x to 3x (with [A] constant), by what factor does the rate increase?

Background

Topic: Rate Laws and Reaction Order

This question tests your ability to use the rate law to predict how changes in concentration affect the reaction rate.

Key Terms and Formulas:

• Rate law:

• Order with respect to B: 2 (second order)

Step-by-Step Guidance

1. Write the initial rate:

2. Write the new rate when [B] = 3x:

3. Set up the ratio:

4. Simplify the expression to find the factor by which the rate increases.

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Q3. For the reaction A + 3B → 2C, how should the rate be expressed?

Background

Topic: Rate Expressions and Stoichiometry

This question tests your understanding of how to relate the rate of change of reactants and products to the overall reaction rate using stoichiometric coefficients.

Key Terms and Formulas:

• General rate expression:

• For A + 3B → 2C: a = 1, b = 3, c = 2

Step-by-Step Guidance

1. Write the general form for the rate based on stoichiometry.

2. Plug in the coefficients for A, B, and C.

3. Identify which expression matches the answer choices.

4. Look for the expression involving (1/2) times the rate of change of C.

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Q4. What is the correct unit for a first-order rate constant?

Background

Topic: Rate Constants and Reaction Order

This question tests your knowledge of how the units of the rate constant depend on the order of the reaction.

Key Terms and Formulas:

• First-order rate law:

• Units of rate: mol L-1 s-1

• Units of [A]: mol L-1

• Units of k:

Step-by-Step Guidance

1. Write the first-order rate law.

2. Set up the units for rate and concentration.

3. Divide the units of rate by the units of concentration to find the units for k.

4. Compare your result to the answer choices.

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Q5. Which statement best describes the graph representing the integrated 2nd order rate law?

Background

Topic: Integrated Rate Laws

This question tests your understanding of how to graphically represent second-order reactions.

Key Terms and Formulas:

• Integrated second-order rate law:

• Plotting vs. yields a straight line with slope .

Step-by-Step Guidance

1. Recall the integrated rate law for a second-order reaction.

2. Identify what is plotted on the y-axis and x-axis.

3. Determine the slope and whether it is positive or negative.

4. Match this to the answer choices.

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Q6. At 25°C, the rate constant for the first-order decomposition of a pesticide solution is 6.40 × 10-3 min-1. If the starting concentration is 0.0314 M, what concentration will remain after 62.0 min?

Background

Topic: First-Order Integrated Rate Law

This question tests your ability to use the integrated rate law for first-order reactions to calculate concentration after a given time.

Key Terms and Formulas:

• Integrated first-order rate law:

• Alternatively:

Step-by-Step Guidance

1. Identify the known values: M, min-1, min.

2. Write the integrated rate law equation.

3. Plug in the values for , , and .

4. Set up the calculation for but stop before computing the final value.

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Q7. The rate law for the reaction 3A → 2B is rate = k[A] with a rate constant of 0.0447 hr-1. What is the half-life of the reaction?

Background

Topic: First-Order Kinetics and Half-Life

This question tests your ability to calculate the half-life for a first-order reaction.

Key Terms and Formulas:

• Half-life for first-order:

• is the rate constant in hr-1

Step-by-Step Guidance

1. Write the formula for half-life of a first-order reaction.

2. Plug in the value for .

3. Set up the calculation for but do not compute the final value.

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Q8. Butadiene, C4H6, dimerizes to C8H12 with rate law rate = 0.014 L/(mol·s) [C4H6]2. What will be the concentration of C4H6 after 3.0 hours if the initial concentration is 0.025 M?

Background

Topic: Second-Order Integrated Rate Law

This question tests your ability to use the integrated rate law for second-order reactions to find concentration after a given time.

Key Terms and Formulas:

• Integrated second-order rate law:

• L/(mol·s), hours (convert to seconds)

Step-by-Step Guidance

1. Convert 3.0 hours to seconds: s.

2. Write the integrated rate law equation.

3. Plug in , , and .

4. Set up the calculation for but stop before computing the final value.

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Q9. The activation energy for the first-order reaction N2O5(g) → 2NO2(g) + (1/2)O2(g) is 102 kJ/mol. The rate constant (k) is 1.35 × 10-4 s-1 at 35°C. What is the value of k at 0°C? (R = 8.314 J/mol·K)

Background

Topic: Arrhenius Equation

This question tests your ability to use the Arrhenius equation to relate rate constants at different temperatures.

Key Terms and Formulas:

• Arrhenius equation:

• Two-point form:

• in J/mol, J/mol·K, in Kelvin

Step-by-Step Guidance

1. Convert temperatures to Kelvin: 35°C = 308 K, 0°C = 273 K.

2. Write the two-point Arrhenius equation.

3. Plug in , , , , and .

4. Set up the calculation for but stop before computing the final value.

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Q10. Calculate the percent by mass of potassium nitrate in a solution made from 45.0 g KNO3 and 295 mL of water. The density of water is 0.997 g/mL.

Background

Topic: Solution Concentration (Percent by Mass)

This question tests your ability to calculate percent by mass for a solute in a solution.

Key Terms and Formulas:

• Percent by mass:

• Mass of water: volume × density

Step-by-Step Guidance

1. Calculate the mass of water: .

2. Add the mass of KNO3 to the mass of water to get total mass of solution.

3. Set up the percent by mass formula.

4. Plug in the values but stop before computing the final percentage.

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Q11. What is the mole fraction of urea in a solution that contains 2.1 mol of urea and 4.4 mol of water?

Background

Topic: Solution Concentration (Mole Fraction)

This question tests your ability to calculate mole fraction for a component in a solution.

Key Terms and Formulas:

• Mole fraction:

• Total moles = moles of urea + moles of water

Step-by-Step Guidance

1. Add moles of urea and water to get total moles.

2. Set up the mole fraction formula for urea.

3. Plug in the values but stop before computing the final mole fraction.

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Q12. Calculate the molality of a solution prepared by dissolving 45.38 g of CdBr2 in 375.0 g of water.

Background

Topic: Solution Concentration (Molality)

This question tests your ability to calculate molality, which is moles of solute per kilogram of solvent.

Key Terms and Formulas:

• Molality:

• Moles of CdBr2: mass / molar mass

• Mass of water in kg: 375.0 g = 0.375 kg

Step-by-Step Guidance

1. Calculate moles of CdBr2 using its molar mass.

2. Convert mass of water to kilograms.

3. Set up the molality formula.

4. Plug in the values but stop before computing the final molality.

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Q13. The solubility of nitrogen gas at 25°C and a nitrogen pressure of 522 mmHg is 4.7 × 10-4 mol/L. What is the value of the Henry's Law constant in mol L-1 atm-1?

Background

Topic: Gas Solubility and Henry's Law

This question tests your ability to use Henry's Law to calculate the constant for gas solubility.

Key Terms and Formulas:

• Henry's Law:

• = concentration (mol/L), = pressure (atm), = Henry's Law constant

• Convert pressure from mmHg to atm:

Step-by-Step Guidance

1. Convert 522 mmHg to atm.

2. Set up Henry's Law equation to solve for .

3. Plug in the values for and but stop before computing the final constant.

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Q14. Which of the following is not a colligative property?

Background

Topic: Colligative Properties

This question tests your understanding of colligative properties, which depend on the number of solute particles, not their identity.

Key Terms and Formulas:

• Colligative properties: vapor pressure lowering, boiling point elevation, freezing point depression, osmotic pressure

• Atmospheric pressure is not a colligative property

Step-by-Step Guidance

1. Recall the four main colligative properties.

2. Identify which property in the list is not affected by solute concentration.

3. Compare the answer choices to the definition of colligative properties.

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Q15. What is the boiling point of a solution prepared by dissolving 42.5 g of barbital (MW = 184.2 g/mol) in 825 g of acetic acid? Kb = 3.07°C/m, boiling point of pure acetic acid = 117.9°C

Background

Topic: Boiling Point Elevation (Colligative Property)

This question tests your ability to calculate boiling point elevation for a solution.

Key Terms and Formulas:

• Boiling point elevation:

• = molality = moles of solute / kg of solvent

• Boiling point of solution = boiling point of pure solvent +

Step-by-Step Guidance

1. Calculate moles of barbital:

2. Convert mass of acetic acid to kg:

3. Calculate molality: moles of barbital / kg of acetic acid

4. Set up the boiling point elevation formula and plug in values but stop before computing the final boiling point.

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Q16. What is the freezing point of a solution prepared from 50.0 g ethylene glycol (C2H6O2) and 85.0 g H2O? Kf of water is 1.86°C/m.

Background

Topic: Freezing Point Depression (Colligative Property)

This question tests your ability to calculate freezing point depression for a solution.

Key Terms and Formulas:

• Freezing point depression:

• = molality = moles of solute / kg of solvent

• Freezing point of solution = freezing point of pure solvent -

Step-by-Step Guidance

1. Calculate moles of ethylene glycol:

2. Convert mass of water to kg:

3. Calculate molality: moles of ethylene glycol / kg of water

4. Set up the freezing point depression formula and plug in values but stop before computing the final freezing point.

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Q17. Which of the following is not soluble in water?

Background

Topic: Solubility

This question tests your understanding of which types of compounds are soluble in water based on their polarity and structure.

Key Terms and Formulas:

• Polar and ionic compounds are generally soluble in water.

• Nonpolar compounds (like vitamin E) are not soluble in water.

Step-by-Step Guidance

1. Identify the polarity of each compound listed.

2. Recall that water is a polar solvent.

3. Determine which compound is nonpolar and thus not soluble.

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Q18. Find the molarity of a 17.0% by mass solution of sodium acetate, CH3COONa (molar mass = 82.0 g/mol) in water. The density of the solution is 1.09 g/mL.

Background

Topic: Solution Concentration (Molarity)

This question tests your ability to convert percent by mass and density to molarity.

Key Terms and Formulas:

• Molarity:

• Percent by mass: grams of solute per 100 g of solution

• Density: mass/volume

Step-by-Step Guidance

1. Assume 100 g of solution: 17 g sodium acetate, 83 g water.

2. Calculate moles of sodium acetate:

3. Calculate volume of 100 g solution using density: mL.

4. Convert volume to liters and set up the molarity formula but stop before computing the final value.

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Q19. Calculate the vapor pressure of a solution prepared by dissolving 0.75 mol of safrole in 950 g of ethanol (MW = 46.07 g/mol). P°ethanol = 50.0 torr at 25°C.

Background

Topic: Vapor Pressure Lowering (Colligative Property)

This question tests your ability to use Raoult's Law to calculate the vapor pressure of a solution.

Key Terms and Formulas:

• Raoult's Law:

• = mole fraction of ethanol

• Moles of ethanol:

Step-by-Step Guidance

1. Calculate moles of ethanol.

2. Calculate total moles (ethanol + safrole).

3. Calculate mole fraction of ethanol.

4. Set up Raoult's Law formula and plug in values but stop before computing the final vapor pressure.

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Q20. 0.102 g of an unknown compound dissolved in 100 mL of water has an osmotic pressure of 28.1 mmHg at 20°C. Calculate the molar mass of the compound.

Background

Topic: Osmotic Pressure and Molar Mass

This question tests your ability to use the osmotic pressure equation to determine molar mass.

Key Terms and Formulas:

• Osmotic pressure:

• = molarity, = 0.0821 L·atm/(mol·K), in Kelvin

• Convert mmHg to atm:

Step-by-Step Guidance

1. Convert osmotic pressure from mmHg to atm.

2. Convert 100 mL to liters.

3. Convert 20°C to Kelvin.

4. Set up the osmotic pressure equation and solve for molarity, then use mass and molarity to find molar mass, but stop before computing the final value.

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