14.1.1 An Introduction to Reaction Rates

Question 1

An Introduction to Reaction Rates

Answer 1

• The average rate for a chemical reaction is the change in the concentration of a substance over time.
• The instantaneous rate for a chemical reaction is the reaction rate at any given point in time.

Question 2

note

Answer 2

• The average rate for a chemical reaction is the change in the concentration of a substance over time.
• This is analogous to the average speed for a car ride. The average speed is simply the distance traveled ( d) divided by the time ( t).
• For example, for a reaction producing oxygen gas (O 2), the rate of production of oxygen gas would be the change in the concentration of oxygen gas ( [O 2 ]) divided by the change in time ( t).
• The average reaction rate is measured in units of molar per second (M/s).
• The instantaneous rate for a chemical reaction is the reaction rate at any given point in time.
  This is analogous to the instantaneous speed for a car ride.
• This is the speed on the speedometer at any given point in time. For example, on a trip with an average speed of 50 miles per hour (mph), the instantaneous rate might be 90 mph at a certain point during the trip.
• The instantaneous rate for a given point in time is the slope of the line tangent to that point on the curve of concentration versus time. This is expressed mathematically as the derivative of the concentration of product with respect to time (d[product]/dt). For example, for a reaction producing oxygen gas, the instantaneous rate is d[O 2 ]/dt.

Question 3

Which of the following describes how the instantaneous reaction rate changes over time during the formation of O2 from the decomposition of N2O5?

Answer 3

The rate decreases to zero as reaction time increases.

Question 4

Examine the potential energy diagram below. Which part of the diagram best represents the domain of kinetics? In other words, the study of chemical kinetics is concerned with which part of the diagram?

Answer 4

region B

Question 5

Which statement does not illustrate the relationship between surface area and reaction rate?

Answer 5

The enzyme maltase speeds up the decomposition of maltose into monosaccharides.

Question 6

Using the graph below, calculate the instantaneous reaction rate for the formation of NO at 100.0 s, and tell whether the instantaneous rate at 100.0 s is faster or slower than the instantaneous rate at 50.0 s.

Answer 6

1.34 × 10^−4 M / s, slower at 100s

Question 7

Hydrogen gas reacts with iodine chloride to form iodine and hydrogen chloride as given by the balanced equation below:

H2(g) + 2ICl(g) → I2(g) + 2HCl(g)

The rate of the reaction can be measured in terms of the rate of decrease of [H2 ]. Using the graph below, calculate the average reaction rate for the time period 0.00 − 2.00 seconds.

Answer 7

0.237 M / s

Question 8

Using the graph below, calculate the average reaction rate for the time period 50 − 200 seconds.

Answer 8

1.1 × 10^−4 M / s

Question 9

Using the graph below, calculate the average reaction rate for the consumption of H2 between 3.00 s and 4.00 s. Is the average rate over this interval faster or slower than the instantaneous rate at 3.00 s?

Answer 9

0.062 M / s, slower than the instantaneous rate at 3.00 s

Question 10

Which of the following inventions or techniques is improperly paired with the reaction it attempts to inhibit?

Answer 10

expiration date on soda can / saccharin decomposition

Question 11

Hydrogen and oxygen can react to form water. Why then, is it possible to have pure hydrogen and pure oxygen present in a balloon without any reaction occurring at all?

Answer 11

Ea for the reaction is quite high

Question 12

If a reaction occurs without any outside intervention, it is said to be what?

Answer 12

spontaneous