Mass Action

Question 1

Mass action: Reaction rate depends on

Answer 1

– concentration of reactants

• higher concentrations give more collisions

– temperature

• higher temperature gives greater energy per collision

– Environment

• solvent
• pH
• catalysts

Question 2

Based on experimental observations the law of mass
action states that:

Answer 2

the rate of a reaction (at a constant temperature) is proportional to the product of the concentrations of the reactants.

Question 3

In order for a reaction to occur…

Answer 3

a collision must occur.

• The collision must be of sufficient energy to break the necessary bonds and be of proper orientation.

Question 4

The number of collisions per unit time can be
expected to

Answer 4

change with the number of molecules of the reactants available.

Question 5

At higher temperatures the number of

Answer 5

collisions is also expected to increase.

• That is, the rate varies as the concentrations
  change

Question 6

Reversible reactions: When two molecules A and B collide…

Answer 6

with one
another in an appropriate orientation, and with
sufficient energy, they can react to form new
molecules – the reaction products, say C and D:

A + B –> C + D

• The potential energy diagram for the bimolecular collision may have the following appearance:
  Reversible reactions

Question 7

As soon as significant concentrations of the product…

Answer 7

molecules C and D are formed, it will inevitably happen that a molecule of C will collide with a molecule of D. If these two molecules collide with one another in an appropriate orientation, and with sufficient energy, they can react to re-form the original
molecules A and B:

C + D –> A + B

• This event can be depicted on the potential energy diagram as:

Question 8

Chemical reactions can take…

Answer 8

place not only in the forward direction but also in the reverse direction.

Question 9

For an exothermic reaction the Ea …

Answer 9

(activation energy) for the reverse
reaction Ea,b is larger than the activation energy for the
forward reaction Ea,f.

Question 10

Any reaction that can proceed to a significant extent

Answer 10

in both the forward and reverse directions is called a reversible
reaction.

*A reversible reaction is denoted as follows:

A + B <—> C + D