CHEM
YEAR 2
, ORDER OF REACTION
This is the exponent/number which describe the change in conc effect on initial rate of reaction
Sometimes increase in conc does not increase rate
0 order- conc has no effect - straight line across y axis
1st order - directly proportional conc and rate increases by the same number - straight line - y=mx+c line
2nd order - exponential if conc doubles rate gets squared shown by a exponential model graph- curved
2nd order - e.g. - if you triple conc rate of reaction increases by 3 squared (9) and etc
Overall sum of orders is when you just add the orders in a reaction together
Finding orders of reaction Finding order of initial B
E.g. So 0.4/0.1 = 4
Initial rate was 0.8 which times by 4 = 3.2
Hence this is a directly proportional relationship and is the 1st order
Finding order of A - changes between 2 and 3
Account for B first - doubles between 2 and 3 hence 3.2 should double
without A being involved - so it becomes 6.4
However it becomes 1.6 with A hence it is smaller by a factor of 4
As 6.4 divided by 1.6 = 4
As A halves rate becomes smaller by ¼ hence it is an exponential
relationship - 2nd order
If you account for A and B you will see no change in initial rate of
reaction when C changes conc between 3 and 4 hence is 0 order
, CONC Vs TIME GRAPHS
Straight line is order 0 curved line is order 1 even more exponential/ curved graph is order 2
To find gradient of the curve you draw a tangent then do the conc/time
To prove orders of reaction you find the gradient at 2 separate points and then compare the relationships with
respect to conc and time - e.g. if one halves and the other halves as well it is first order
, HALF LIFE
Finding t ½
-choose any point on
y axis
This is the time taken for a conc of a reactant to decrease by half -half it
Used in various practicals to deduce the order -its difference in time
is its half life
How to work out half life from graph
Choose a conc - in this case e.g. 1.2
Half the conc
See what time it is at in this case 0.6 conc = 60 sec
Half the conc again - 0.3
At 0.3 it is at 30 sec
-As time is getting halved each time conc is getting halved this is 0 order
Half life is written as t ½ decreases over time
-For 1st order time stays the same as conc halves and is t ½ stays
constant
-For 2nd order as conc halves time doubles which is written as t ½
increases over time
Equation to find the rate constant, K, can only be used for overall order of a 1st order of reaction
Equation = ln2 / t ½
T ½ of course is the half life in seconds for 1st order this is constant always
YEAR 2
, ORDER OF REACTION
This is the exponent/number which describe the change in conc effect on initial rate of reaction
Sometimes increase in conc does not increase rate
0 order- conc has no effect - straight line across y axis
1st order - directly proportional conc and rate increases by the same number - straight line - y=mx+c line
2nd order - exponential if conc doubles rate gets squared shown by a exponential model graph- curved
2nd order - e.g. - if you triple conc rate of reaction increases by 3 squared (9) and etc
Overall sum of orders is when you just add the orders in a reaction together
Finding orders of reaction Finding order of initial B
E.g. So 0.4/0.1 = 4
Initial rate was 0.8 which times by 4 = 3.2
Hence this is a directly proportional relationship and is the 1st order
Finding order of A - changes between 2 and 3
Account for B first - doubles between 2 and 3 hence 3.2 should double
without A being involved - so it becomes 6.4
However it becomes 1.6 with A hence it is smaller by a factor of 4
As 6.4 divided by 1.6 = 4
As A halves rate becomes smaller by ¼ hence it is an exponential
relationship - 2nd order
If you account for A and B you will see no change in initial rate of
reaction when C changes conc between 3 and 4 hence is 0 order
, CONC Vs TIME GRAPHS
Straight line is order 0 curved line is order 1 even more exponential/ curved graph is order 2
To find gradient of the curve you draw a tangent then do the conc/time
To prove orders of reaction you find the gradient at 2 separate points and then compare the relationships with
respect to conc and time - e.g. if one halves and the other halves as well it is first order
, HALF LIFE
Finding t ½
-choose any point on
y axis
This is the time taken for a conc of a reactant to decrease by half -half it
Used in various practicals to deduce the order -its difference in time
is its half life
How to work out half life from graph
Choose a conc - in this case e.g. 1.2
Half the conc
See what time it is at in this case 0.6 conc = 60 sec
Half the conc again - 0.3
At 0.3 it is at 30 sec
-As time is getting halved each time conc is getting halved this is 0 order
Half life is written as t ½ decreases over time
-For 1st order time stays the same as conc halves and is t ½ stays
constant
-For 2nd order as conc halves time doubles which is written as t ½
increases over time
Equation to find the rate constant, K, can only be used for overall order of a 1st order of reaction
Equation = ln2 / t ½
T ½ of course is the half life in seconds for 1st order this is constant always
