Rate Equations

Question 1

What does a rate equation show

Answer 1

How changes in the concentrations of reactants affect the rate of reaction, shows the molecules that are reactants in rate determining step (slowest)

Question 2

What does each letter stand for in rate=k[A]^x[B]^y

Answer 2

-constant k is rate constant
-[A] and [B] represent the concentrations of reactants in mol/dm3
-powers x and y are the reaction orders with respect to A and B in equation

Question 3

What is the overall order of a reaction

Answer 3

The sum of the orders for all the substances that appear in the rate equation

Question 4

What does factor does rate constant (k) vary with

Answer 4

Temperature

Question 5

What is a first order reactant

Answer 5

Reaction is first order with respect to a reactant if the rate of reaction is proportional to concen of that reactant, raised to power one in the rate equation

Question 6

What type of line is on graph for first order reaction for concen rate

Answer 6

Straight line passing through the origin

Question 7

What is the half-life of a reaction

Answer 7

The time for the concentration of one of the reactants to fall by half

Question 8

What is a second order reactant

Answer 8

If the rate of reaction is proportional to the concentration of that reaction squared, raised to the power two in the rate equation for that reactant

Question 9

What does doubling concentration of X raised to power 2 in rate equation do to rate

Answer 9

Increases rate by factor of four

Question 10

What does concentration-time graph look like for second order reaction and how to find gradient

Answer 10

Curve, draw tangents to curve to find gradient

Question 11

What is a zero order reaction and what does concentration-rate graph look like

Answer 11

When concentration of that reactant does not affect the rate of reaction, raised to the power zero
-graph is straight line across

Question 12

What do the units of the rate constant depend on

Answer 12

The overall order of the reaction

Question 13

Does the half-life of a first order reaction change depending on starting concentration

Answer 13

No it is the same whatever the starting concentration

Question 14

How to find the half-life of a second order reaction

Answer 14

Half-life is inversely proportional to the starting concentration

Question 15

If reactant involved in mechanism after rate determining step what is its order and what about before

Answer 15

Zero, if before either first or second

Question 16

Units of rate constant for zero order reaction

Answer 16

mol dm^-3 s^-1

Question 17

Units of rate constant for first order reaction

Answer 17

s^-1

Question 18

Units for rate constant for second order reaction

Answer 18

Mol^-1 dm^3 s^-1

Question 19

Units for rate constant for third order reaction

Answer 19

Mol^-2 dm^6 s^-1

Question 20

How to get units for rate constant

Answer 20

Rearrange to get rate/concens and unit for rate is moldm^-3 s^-1

Question 21

What do concentration time graphs look like for first and second order reactions

Answer 21

Curved

Question 22

Is half life constant throughout first order reaction

Answer 22

Yes

Question 23

How are rate equations determined

Answer 23

Experimentally, cannot be found from stoichiometric equations

Question 24

What does and doesn’t feature in the rate equation

Answer 24

Products and catalysts may feature in rate equations but intermediates do not feature (generated in slowest step and reactants in another step)

Question 25

What is the overall order of reaction

Answer 25

The sum of the powers of the reactants in a rate equation

Question 26

Why wouldn’t clock reaction be order of reaction with respect to iodide ions as 5

Answer 26

Because the chance of five or more ions colliding in rate determining step is negligible