Honors Unit 7 Reaction Kinetics

What is the unit of reaction rate in kinetics?

• mol/L
• L/s
• mol/L·s
• mol/s
• L/mol·s

Answer explanation

Rate is typically expressed as mol/L·s.

Which expression represents the rate of a disappearing reactant A?

• Rate = Δ[A]/Δt
• Rate = -Δ[A]/Δt
• Rate = [A]/t
• Rate = Δt/Δ[A]
• Rate = -t/[A]

Answer explanation

For disappearing reactants, rate is negative: Rate = -Δ[A]/Δt.

What is the average rate if [A] drops from 0.80 M to 0.20 M in 10 s?

• 0.06 M/s
• 0.08 M/s
• –0.06 M/s
• –0.08 M/s
• 0.60 M/s

Answer explanation

Average rate = (0.80–0.20)/10 = 0.06 M/s.

In the reaction 2A + B → 3C, if A disappears at 0.10 M/s, what is the rate of formation of C?

• 0.05 M/s
• 0.10 M/s
• 0.15 M/s
• 0.20 M/s
• 0.30 M/s

Answer explanation

3 mol C / 2 mol A × 0.10 = 0.15 M/s.

Why is the rate of reactant disappearance often expressed with a negative?

• To show the math is wrong
• To indicate volume loss
• To correct for temperature
• To reflect the decreasing concentration
• To match product formation

Answer explanation

Reactant concentration decreases over time.

Choose all valid ways to define rate in a reaction.

• Rate = Δ[Product]/Δt
• Rate = –Δ[Reactant]/Δt
• Rate = [A]/t
• Rate = Δ[Conc.]/Δt
• Rate = Δt/Δ[Conc.]

Answer explanation

Rates are expressed as change in concentration per time.

What is the difference between average and instantaneous rate?

• Average is slope at a point; instantaneous is over time
• Average is over a time interval; instantaneous is slope at a point
• They are always equal
• One is for gases only
• Neither is measurable

Answer explanation

Average = over interval; instantaneous = slope at specific point.

Which rate is measured when t = 0?

• Final Rate
• Instantaneous Rate
• Average Rate
• Initial Rate
• Steady-State Rate

Answer explanation

Initial rate is the rate at t = 0.

If B disappears at 0.05 M/s in 2A + B → 3C, what is the rate of appearance of C?

• 0.05 M/s
• 0.075 M/s
• 0.15 M/s
• 0.10 M/s
• 0.025 M/s

Answer explanation

1 mol B → 3 mol C → 3×0.05 = 0.15 M/s.

Fill in the blank: Reaction rate compares concentration change over ______.

Answer explanation

Rate is the change in concentration per unit time.