Rates of Reactions

Question 1

Define what is the rate of a chemical reaction

Answer 1

The rate of a chemical reaction is defined as the change in concentration of a reactant or product compared with the period of time taken for the change to occur.

Question 2

Rate =

Answer 2

time taken for the change to occur

Question 3

What is a measure of how quickly a reaction happens?

Answer 3

The rate, or speed, of a reaction is a measure of how quickly a reaction happens.
* Some reactions, like explosions, are very quick – they finish within seconds.
* Some reactions, like rusting, are very slow – they finish in months or years.
* Some reactions, like baking a cake, are somewhere in between – they finish in minutes or hours.

Question 4

We can tell if a reaction is occurring quickly or slowly by…

Answer 4

monitoring a visible or measurable quantity.
For example:
* The change in mass in a given time if a gas is being given off
* The volume of gas given off in a certain amount of time
* The appearance of a precipitate
* The change in colour intensity, pressure, temperature or pH if these
are changing as the reaction proceeds

Question 5

During any reaction, the concentration of reactants…

Answer 5

decreases at the same rate as the conc of products increasess

Question 6

• In order for reactants to be converted to products,

Answer 6

effective collisions must occur
An effective collision requires that:
1) Particles must collide
2) Collisions must occur with an energy above the value of the
Activation Energy for the reaction
3) Collisions must occur with the correct orientation

Question 7

define activation energy

Answer 7

Activation energy, in chemistry, is the minimum amount of energy that is required to activate atoms or molecules to a condition in which they can undergo chemical transformation.

Question 8

The concentration of a reactant…

Answer 8

decreases with time

Question 9

The concentration of a product…

Answer 9

increases with time

Question 10

describe the rate curve

Answer 10

• At the beginning of the reaction, reactant concentration is the highest and the particles collide frequently, so rate is fast, there is a steep gradient to the curve.
• As reactants are used up, the concentrations decrease and particles collide less frequently; the reaction rat is slower and the gradient becomes less steep.
• Eventually when all reactant has been used up, no more collisions occur and gradient is flat (0).

Question 11

Rate of reaction at a given time is equal to

Answer 11

the gradient of the tangent to the curve at that time.

Question 12

list the property changes in the chemical reactions

Answer 12

• volume of gaseous product
• colour intensity
• amount of precipitate formed
• decrease in mass (if gas is evolved)