Rates of reaction

Question 1

Rate of reaction definition?

Answer 1

The change in concentration of a reactant or product in unit time

Question 2

What is rate of reaction measured in?

Answer 2

mol dm^-3 s^-1

Question 3

What does higher pressure do to the rate of reaction?

Answer 3

Increases it, as more frequent collisions

Question 4

How can a chemical reaction be monitored?

Answer 4

Colour change
Change in mass
Volume of gas produced
Conductivity

Question 5

Rate of reaction formula?

Answer 5

Change in concentration/ change in time

Question 6

How can you measure the rate of reaction at a certain point on a concentration- time graph?

Answer 6

Find the gradient of the tangent

Question 7

Catalyst definition?

Answer 7

A substance that increases the rate of a chemical reaction, without being used up in the process. By providing an alternative route for the reaction with lower activation energy

Question 8

What’s a heterogeneous catalyst?

Answer 8

One in a different physical state from the reactants, most frequently gaseous reactants, and solid catalyst

Question 9

What’s a homogenous catalyst?

Answer 9

One in the same physical state as the reactants, normally aqueos of gaseous state

Question 10

What are the sustainable and economic importance of catalysts?

Answer 10

Reduce energy consumption, and therefore reduced effect on environment
Also less energy used in heating reaction, so increased profits

Question 11

How to draw a Boltzman distribution?

Answer 11

Curve starts at (0,0)
Goes up in straight line then slopes down, then slopes off
X axis= kinetic energy
Y axis= Number of particles
Label the activation with a vertical line at tail

Question 12

What does the area under a Boltzman distribution represent?

Answer 12

Total number of particles in the system

Question 13

Which proportion of molecules have more than the kinetic energy and therefore can react?

Answer 13

The area after the EA line

Question 14

What happens to the Boltzman distribution if you increase the temperature?

Answer 14

Peak gets lower, and moves to a higher energy

Tail will there be higher when passing the EA

Question 15

What happens to the proportion of molecules with at least the activation energy when the temperature increases?

Answer 15

Increases

Question 16

What happens to Boltzman distribution when you add a catalyst?

Answer 16

EA decreases

Question 17

Why does increasing the concentration of reactant or pressure of reactant increase rate of reaction?

Answer 17

More particles per unit volume, so more frequent collisions

Question 18

How does grinding the solid reactant into a powder increase the rate of reaction?

Answer 18

Increased surface area of contact, so more frequent collisions

Question 19

What is meant by activation energy, and why do most chemical reactions require one?

Answer 19

Minimum energy required to start a reaction (by the breaking of bonds), and most reactions require bonds to be broken in reactant molecules

Question 20

Definition of rate equation for the reaction A + B = C ?

Answer 20

Rate = K ((A)^m)((B)^n)
where m and n are the order of reaction (0, 1 or 2)
Rate= rate in mol dm^-3 s^-1
K= rate constant
A and B are the concentrations of the chemicals in mol dm^-3

Question 21

Definition of order of reaction?

Answer 21

The power to which the concentration of reactant is raised in the rate equation

Question 22

Definition of rate constant?

Answer 22

The constant that links the rate of reaction with the concentrations of the reactants raised to the power of their orders in the rate equation

Question 23

Zero order reaction on a Rate-conc graph?

Answer 23

Horizontal line

Question 24

1st order reaction on a Rate-conc graph?

Answer 24

starts at origin and is diagonal line

Question 25

2nd order reaction on a Rate-conc graph?

Answer 25

Starts at origin, is curved line, gradient increases

Question 26

Definition of half life?

Answer 26

The time taken for the concentration of a reactant to reduce by half?

Question 27

How to determine what order a reaction is on a conc-time graph?

Answer 27

0 order- diagonal line going down
1st order- curved line going down, half life is constant
2nd order- steeper curved line going down, half life isn’t constant

Question 28

How to calculate k from the half life?

Answer 28

k = ln2/ (Half life)

Only for first order

Question 29

Definition of initial rate of reaction?

Answer 29

The change in concentration of a reactant or product per unit time at the start of a reaction (time = 0)

Found with a tangent

Question 30

Why is initial rate of reaction a good measure?

Answer 30

Concentrations of all reactants known

Temperature is known and controlled

Question 31

How to work out orders of reaction from various experiments in a table?

Answer 31

Look at 2 experiments where all concentrations are the same except 1, and see what change this has done to the initial rate
If you conc has doubled and initial rate is the same then is order 0
If rate has doubled is 1st order
If rate has multiplied by 4 then its 2nd order
Can use fact that you’ve worked out zero order, to work out other unknowns

Put values into rate equation to work out k

Question 32

What happens to rate constant if temp is increased?

Answer 32

It is increased, as a greater proportion of collisions will be successful

Question 33

What happens to rate constant if a catalyst is added?

Answer 33

It will increase, as catalyst provides an alternative route with lower activation energy so greater proportion of collisions will be successful

Question 34

What’s a clock reaction?

Answer 34

Where the time is measured for a specific change to occur, time is inversely proportional to the rate of reaction

Question 35

What is the rate determining step?

Answer 35

The slowest step in a reaction mechanism of a multi step reaction

Question 36

How to tell if a reaction is single step?

Answer 36

If the reactants in the normal balanced equation match the rate equation

Question 37

What’s the Arrhenius equation?

Answer 37

k= Ae^(Ea/(RT)

k = rate constant
A= frequency factor
e= mathematical quantity
Ea= activation energy
R = gas constant
T= temp in kelvin

Question 38

Logarithmic form of Arrhenius equation?

Answer 38

ln K = -Ea/RT + ln A

-Ea/RT = gradient
ln A = intercept