Rates

Question 1

Rate of reaction

Answer 1

Change of concentration over time

Question 2

Order

Answer 2

The effect the concentration of the reactant has on the rate

Question 3

Overall order

Answer 3

The sum (addition) of the orders with respect to each reactant.

Question 4

Rate constant

Answer 4

A proportional constant, which multiplies with the concentration and orders to equal the rate.

Question 5

Half-life

Answer 5

The time for half of the reactant to be used up.

Question 6

Rate-determining step

Answer 6

The slowest step in the series of steps which make a reaction

Question 7

Example of a rate equation

Answer 7

Rate = k [A]^m {B]^n

Question 8

Zero order

Answer 8

When the concentration of a reactant has no effect on the rate {A]^0

Question 9

First order

Answer 9

The rate depends on the concentration raised to the power of one, so if the concentration is tripled the rate is also tripled. [A]^1

Question 10

Second order

Answer 10

The rate depends on the concentration raised to the power of two, so if the concentration is tripled the rate increases by a factor of 9. [A]^2

Question 11

Determining the units of rate constant K

Answer 11

Put the units of the rate and divide it by the units of the concentration, if it is second order you divide it by the units squared

Question 12

How to find out K

Answer 12

Divide the rate by the concentration, if it is a second order reaction you square the concentration

Question 13

How to find out orders

Answer 13

You compare the initial rate at various concentrations and see how much the rate changes, i.e. does it double or is it squared.

Question 14

How can you monitor rate

Answer 14

Colorimeter, mass loss, gas collected

Question 15

Shape of a zero order concentration-time graph

Answer 15

Straight light with a negative gradient

Question 16

Shape of a first order concentration-time graph

Answer 16

Curve down with decreasing gradient over time, less steep then second

Question 17

Shape of a second order concentration-time graph

Answer 17

Curve, gradient decreases over time, more steep then first

Question 18

Rates and half life

Answer 18

First order reactions have a constant half life

Question 19

How to calculate rate from a graph

Answer 19

Draw a tangent at a particular concentration, the gradient of the tangent is equal to the rate.

Question 20

Calculating rate constant from half life

Answer 20

K = ln2 / half life

Question 21

Zero order rate-concentration graph

Answer 21

Horizontal straight line with no gradient, y-intercept is K. Reaction rate does not change with concentration

Question 22

First order rate-concentration graph

Answer 22

Straight line that goes through the origin. Rate constant an be determined by measuring the gradient

Question 23

Second order rate-concentration graph

Answer 23

An upward curve with an increasing gradient. Rate constant can be determined by drawing a second graph of the rate against concentration squared. This results in a straight line going through the origins, the gradient equals the rate constant

Question 24

How do you if a rate mechanism and rate determining step is correct?

Answer 24

The rate equation only includes reacting species involved in the rate determining step. The orders in the rate equation match the number of species involved in the rate determining step.

Question 25

The effect of temperature on rate constant

Answer 25

As temperature increases the rate and rate constant increase in value.

Question 26

Why does increased temperature increase the rate constant

Answer 26

The Boltzman distribution is shifted to the right so more particles have an energy above the activation energy. Particles move faster and increase more frequently

Question 27

The Arrhenius equation

Answer 27

``` K = Ae^-Ea/Rt R= gas constant T=temperature Ea= activation energy A = frequency factor ```

Question 28

Logarithmic form of the Arrhenius equation

Answer 28

ln(k) = (-Ea / RT) + ln A

Question 29

How to get values for Arrhenius equation from a graph

Answer 29

Gradient is -Ea/R | Y intercept is A

Question 30

How does increasing the concentration affect the rate of reaction

Answer 30

An increase in concentration increases the rate of reaction. An increase in concentration increases the number of particles in the same volume. The particles are closer together and collide more frequently. In a given period of time there will be more effective collisions and an increased rate of reactions.

Question 31

Effect of pressure on the rate of reaction

Answer 31

As the pressure increases the concentration of gas molecules increases as the same number of gas molecules occupy a smaller volume. The gas molecules are closer together and collide more frequently leading to more effective collisions in the same amount of time.

Question 32

How to measure reaction rate

Answer 32

You draw a tangent and calculate the gradient. The gradient is equal to the rate

Question 33

Catalyst

Answer 33

Increases the arte of reaction without being used up itself