Physical - Rate Equations

Question 1

What is the rate equal to?

Answer 1

The rate constant (k) multiplied by the concentration of each reactant raised a certain whole number powers

Question 2

What does it mean if reactant is zero order?

Answer 2

Some reactants may be zero order, which means they do not appear in the rate equation as [X]^0 = 1

Question 3

What is the rate equation for a general reaction?

Answer 3

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

m is the order of reaction with respect to reactant A.
n is the order of reaction with respect to reactant B.

Question 4

What does it mean if the order with respect to a reactant is 0?

Answer 4

If the concentration of a reactant changes and the rate stays the same.

So if [A] doubles the rate will stay the same. If [A] triple the rate will stay the same.

Question 5

What does it mean if the order with respect to a reactant is 1?

Answer 5

The rate is proportional to the concentration of a reactant.

So if [A] doubles the rate will double. If [A] triple the rate will triple

Question 6

What does it mean if the order with respect to a reactant is two?

Answer 6

If the rate is proportional to the concentration of a reactant squared.

So if [A] doubles the rate will be 2^2=4 times faster. If [A] triples the rate will be 3^2=9 times faster

Question 7

How does temperature affect the rate constant?

Answer 7

As the temperature increases, the rate constant increases

Question 8

What is the Arrhenius equation?

Answer 8

The Arrhenius equation links the rate constant with activation energy and temperature

Question 9

What is the Arrhenius equation?

Answer 9

k = Ae^-Ea/RT

• k is the rate constant
• A is the Arrhenius constant
• e is a mathematical constant (e^1 on calculator)
• Ea is the activation energy
• R is the gas constant
• T is the temperature measured in K

Question 10

What are the methods for determining the rate of reaction?

Answer 10

• A gaseous product which can be monitored using a gas syringe
• A coloured reactant or product which can monitor using colorimetry
• A directly measurable reactant or product ie. H+ ions or OH- ions by measuring pH using a pH meter

Question 11

What is the rate determining step?

Answer 11

The right determining step is the slowest step and it dictates the overall rate of the reaction.

The species that react in the rate determining step are the species which are present as concentrations with non-zero orders in the rate equation.

Reactants in the overall equation which have zero order are not involved in the rate determining step