Collision theory / factors affecting r.o.r

Question 1

In order to react (3):

Answer 1

1) Particles of the reacting substances must collide with eachother to break old bonds in the reactants, and form new bonds in the products.
2) The colliding particles must produce sufficient energy to break the old bonds in the reactants.This energy is called activation energy. Not all collisions produce the required energy, therefore not all collisions result in a reaction occuring
3) reactant particles must collide with the correct orientation so that the enrgy produced by the collision can be passed on to the bonds to be broken.

Question 2

Concentration: (of reactants)

Answer 2

When concentration increases, the number of reacting particles per unit volume increases.
Thus the frequency of effective collisions increases and hence rate of reaction increases.

Question 3

Pressure (for gases only)

Answer 3

When pressure increases, the number of reacting gaseous particles per unit volume increases. Thus, the frequency of effective collisions increases and hence, rate of reaction increases.

Question 4

Temperature

Answer 4

When temperature increases, the average kinetic energy of reacting particles increases.
More collisions can occur with energy above the required activation energy (major effect)
Thus, the frequency of effective collisions increases, and hence, rate of reaction increases.
Also collisions occur more frequently (monir effect)
nb: the rate of reaction approx. doubles for every rise in temp of 10 degrees

Question 5

Surface Area

Answer 5

When surface area increases, (most usually powdered) the frequency of effective collisions increase and hence, the rate or reaction increases

Question 6

Catalyst

Answer 6

Catalyst are substances that speed up a chemical reaction but remains chemically unchanged at the end of the reaction. Hence, catalysts provide an alternative pathway with lower activation energy for reaction to take place.
Therefore, the frequency of effective collisions increases, and hence the increase in rate of reaction.

Question 7

Rate of reaction increases if:

Answer 7

The temp is increases
the conc of a dissolved reactant is increased
the pressure of a reacting gas is increased
solid reactants are broken into smaller pieces
a catalyst is used