Rate graphs and Orders

Question 1

What is continuous monitoring?

Answer 1

Making continuous measurements of reactants over the course of a reaction.

Question 2

What are the three methods of continuous monitoring?

Answer 2

• monitoring by gas collection
• monitoring by mass loss
• monitoring rate with a colorimeter

Question 3

How do you monitor rate with a colorimeter?

Answer 3

• Monitor the rate by the dissapearance of a coloured solution over a period of time by colorimeter values

Question 4

What is the shape of a zero order reactant on a concentration time graph?

Answer 4

A straight line with a negative gradient

Question 5

What is the shape of a first order reactant on a concentration time graph?

Answer 5

A downward curve with a decreasing gradient over time.
As the gradient decreases with time, the reaction gradually slows down
The rate of the first order can then be found by the half life

Question 6

What is half life?

Answer 6

The time taken for half of a reactant to be used up.

Question 7

What half life do first order reactants have?

Answer 7

A constant half life

Question 8

What are the two methods of determining the rate constant for a first order reaction?

Answer 8

1. Calculating the rate constant from rate of a reaction
   This can be done by drawing a tangent to the curve on the concentration time graph at a particular concentration. The gradient is therefore the rate of reaction.
2. Calculating the rate constant from half - life
   This can be done by finding a constant half life and using the equation
   K = in2/t1/2

Question 9

What is the shape of a zero order reactant on a rate concentration graph?

Answer 9

A horizontal line with a zero gradient

Question 10

How do you find the rate constant of a zero order reactant on a rate concentration graph?

Answer 10

The intercept on the y axis gives the rate constant

Question 11

What is the shape of a first order reactant on a rate concentration graph?

Answer 11

A straight line through the origin

Question 12

How do you find the rate constant of a first order reactant on a rate concentration graph?

Answer 12

The gradient of a straight line graoh

Question 13

What is the shape of a second order reactant on a rate concentration graph?

Answer 13

An upward curve with an increasing gradient

Question 14

How do you find the rate constant of a second order reactant on a rate concentration graph?

Answer 14

To determine k you would need to plot a second graph of rate against concentration squared and then finding the gradient of this straight line

Question 15

What is the initial rates method?

Answer 15

• Initial rate = the instantaneous rate of a reaction when t=0
• The initial rate can be found by measuring a gradient of a tangent at t = 0
• A clock reaction can then be used to find the initial rate
• You can then assume that the rate of reaction is the same as the initial rate
• initial rate = 1/T

Question 16

What is the iodine clock reaction?

Answer 16

• As aqueous iodine is orange/brown coloured, the time for an iodine colour appearance can be measured
• Starch can then be added as it forms a blue/black colour in the presence of iodine
• Then measure how long it takes for a blue/black colour to appear
• Initial rate = 1/T