Topic 9 Rates of reaction

Question 1

How to speed up the rate of reaction

Answer 1

-Use a catalyst
-Increase concentration
-Increase temperature
-Increase surface area
-Increase pressure

Question 2

Rate of reaction equation

Answer 2

Change in mass of reactant or product
__________________________________________
Time

Question 3

Maxwell Boltzmann distribution

Answer 3

Question 4

Boltzmann distribution points

Answer 4

1) Shows the distribution of molecular energies
2) Allows us to represent the fraction of molecules in a sample with sufficient energy to react (by marking the activation energy)
3) There are no molecules with zero energy (the curve approaches the x-axis asymptotically)
4) The distribution changes at different temperatures as the distribution of energy of the molecules changes

Question 5

Effects of changing temperature

Answer 5

Question 6

Effects of changing T points

Answer 6

1) The total area under the curve is the same for both temperatures
2) The peak is lower and the distribution is displaced to the right for higher temperatures
3) Ea is the same but a higher fraction of molecules have energy greater than Ea at the higher temperature (the area under the curve is larger)

Question 7

Reactions in solution

Answer 7

-In the gas phase, molecules move at high speeds and frequently collide with each other
-In solute, molecules are more packed together

Question 8

Low-medium concentrations reactions in a solution

Answer 8

-Most of the solution is solvent so the reacting molecules are surrounded by solvent molecules
-They are said to be trapped in a ‘solvent cage’
-This increases the collision rate between solute molecules and, if they have sufficient energy, they may react (this is because sometimes the number of molecules become trapped in the same solvent cage).

Question 9

Lower activation energy

Answer 9

When a reaction has lower activation energy, a higher fraction of the molecules have energy equal to or greater that activation energy therefore we get more successful collisions.

Question 10

The most common type of catalyst used in industry

Answer 10

A heterogenous catalyst
(that is in a different phase to that of the reactants, eg. in the Haber process reactants are in the gas phase but the catalyst is solid iron)

Question 11

Steps in catalyst

Answer 11

1) Adsorption (the attraction of molecules onto the surface of a solid)
2) Weakening of the bonds
3) Desorption (the release of an absorbed substance from a surface).

Question 12

What are the two reasons to use a catalyst?

Answer 12

1) A catalyst increases rate of reaction so more product is made in a given time = more to sell
2) It allows reactions to occur at lower temperatures, this reduces energy costs.