Q: Which of the following is the correct formula for calculating the average rate of a reaction based on the change in mass of a reactant over time?

$$\text{Average Rate} = \frac{\text{Change in Mass}}{\text{Change in Time}}$$

Q: If a reaction is monitored by measuring the volume of gas produced, which of the following would NOT be a valid way to express the rate?

$$\text{Rate} = \text{Time (s)} \div \text{Volume of gas (cm}^3\text{)}$$

Q: Which of the following is the correct way to calculate the instantaneous rate at $$t = 100 s $$using the data points at $$t = 80 s$$ ($$1.40 g CO$_2) $$and $$t = 120 s$$ ($$1.80 g CO$_2$$)?

$$\text{Instantaneous Rate} = \frac{1.80 - 1.40}{120 - 80}$$

Question 1

Which of the following best describes the initial rate of a chemical reaction?

Accepted Answer

The rate measured at the very start of the reaction, when reactant concentrations are at their highest.

Question 2

A student collects the following data for a reaction: At $$t = 0 s$$, $$0 g of CO$_2 is $$lost; at $$t = 40 s$$, $$0.80 g of CO$_2 is $$lost. What is the average rate of CO$$_2$$ loss during this period?

Accepted Answer

$$0.02$$ 	ext{ g/s}$

Question 3

Which of the following is the correct formula for calculating the average rate of a reaction based on the change in mass of a reactant over time?

Accepted Answer

$$	ext{Average Rate} = \frac{	ext{Change in Mass}}{	ext{Change in Time}}$$

Question 4

Why is the initial rate of a reaction typically the fastest?

Accepted Answer

Because the concentration of reactants is at its maximum at the start.

Question 5

A reaction produces a gas that is collected over time. If the mass of the reactant decreases from $$2.50 g to$$ $$0.00 g in$$ $$300 s$$, what is the average rate of the reaction?

Accepted Answer

$$0.0083$$ 	ext{ g/s}$

Question 6

Which method would you use to determine the rate of reaction at exactly $$100$$ seconds?

Accepted Answer

Draw a tangent to the curve at $$100 s $$and calculate its slope.

Question 7

If a reaction is monitored by measuring the volume of gas produced, which of the following would NOT be a valid way to express the rate?

Accepted Answer

$$	ext{Rate} = 	ext{Time (s)} \div 	ext{Volume of gas (cm}^3	ext{)}$$

Question 8

A student wants to know how changing the concentration of a reactant affects the reaction rate. Which rate should they focus on?

Accepted Answer

Initial rate

Question 9

Why must the sign of the slope be converted when calculating the rate from a reactant consumption graph?

Accepted Answer

Because rates are always reported as positive values.

Question 10

Which scenario best illustrates when it is preferable to use the average rate instead of the initial rate?

Accepted Answer

When the reaction is too fast to accurately measure the initial rate.

Question 11

Given the following data: At $$t = 80 s$$, $$1.40 g CO$_2$$ lost; at $$t = 120 s$$, $$1.80 g CO$_2$$ lost. What is the instantaneous rate at $$t = 100 s$$?

Accepted Answer

$$0.01$$ 	ext{ g/s}$

Question 12

Which of the following is NOT a physical quantity that can be used to measure the rate of a chemical reaction?

Accepted Answer

Change in atomic number

Question 13

A reaction is monitored by measuring the time it takes for a precipitate to obscure a mark beneath a beaker. What is this method called?

Accepted Answer

Turbidity method

Question 14

If you only need to know the rate of a reaction at a single, specific time, what is the minimum number of measurements you need?

Accepted Answer

Two measurements: one before and one after the specific time.

Question 15

Which of the following best explains why the rate of a reaction decreases as it proceeds?

Accepted Answer

Reactant concentrations decrease, leading to fewer collisions.

Question 16

A student collects gas through a delivery tube, but there is a delay in collecting data. Which rate is most appropriate to calculate?

Accepted Answer

Average rate

Question 17

Which of the following is the correct way to calculate the instantaneous rate at $$t = 100 s $$using the data points at $$t = 80 s$$ ($$1.40 g CO$_2) $$and $$t = 120 s$$ ($$1.80 g CO$_2$$)?

Accepted Answer

$$	ext{Instantaneous Rate} = \frac{1.80 - 1.40}{120 - 80}$$

Calculating Reaction Rates: Measuring the Speed of Chemical Reactions

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