The Kinetic Molecular Theory states that matter is made up of particles that are always in constant motion and that the particles move more quickly at higher temperatures.

From this theory came the COLLISION MODEL for chemical reactions. According to the collision model there are two ways to make a chemical reaction go faster:

1)    Increase the number of collisions.
2)     Increase the fraction of collisions that are effective.

The COLLISION MODEL can be used to help us understand how (a) temperature,  (b) concentration,  (c) surface area,  and  (d)  catalysts  affect the rate of a reaction.

Generally an increase in temperature increases the reaction rate.
What Temperature Does:
(i)     Increases the frequency of collisions
At a high temperature the particles move faster and therefore collide more often.

(ii)     Increases the number of collisions that have more than the amount of energy required for the reaction to occur
Faster moving particles have more energy.

When more molecules are packed together in a smaller space, they are more likely to collide with each other, thereby causing the reaction to go faster.

As the concentration increases, the rate of the reaction increases.

Surface area is the amount of area of a sample of matter that is visible and able to react. Increasing the amount of surface area increases the number of particles that are available to collide and therefore react.

As the surface area increases, the rate of the reaction increases.

(d)     CATALYSTS:
A catalyst is a substance that increases the rate of a chemical reaction without being consumed by the reaction.

A catalyst provides an easier way for the chemical reaction to occur. It does this by decreasing the amount of collision energy that the particles need to react.

Therefore a catalyst makes the reaction go faster.

Usually when a physical change or a chemical change occurs energy is either released to the surroundings or absorbed from the surroundings. This results in two kinds of changes.

Exothermic Change: A physical change or chemical change that releases heat (energy) to the surroundings. Exothermic changes feel warm or hot.

Examples:     1) Dissolving Drano (drain cleaner) in water.
2) Burning magnesium metal.

Endothermic Change: A physical change or chemical change that absorbs heat (energy) from the surroundings. Endothermic changes feel cool or cold.

Examples:     1)     Dissolving ammonium chloride in water.
2)     Mixing ammonium thiocyanate and barium hydroxide octahydrate.

ACID: a compound that dissolves in water to produce hydrogen ions in the solution.

hydrochloric acid  ®   hydrogen ions   +   chloride ions
HCl(aq)      ®             H+(aq)         +        Cl-(aq)
Note:     aq stands for aqueous or dissolved in water.

BASE: a compound that dissolves in water to produce hydroxide ions in the solution.

sodium hydroxide   ®   sodium ions   +   hydroxide ions
NaOH(aq)      ®           Na+(aq)      +       OH-(aq)

INDICATOR: –     a substance that turns a different colour in acids and bases.
– used for determining if a substance is acidic or basic.



1)       sour taste
2)       react with some metals to produce hydrogen gas
3)       a good conductor of electricity in solution
4)       reacts with a base to produce a salt and water
5)       Indicators:
(a)  blue litmus turns red
(b)  pink phenolphthalein turns colourless
(c)  neutral (green) bromthymol blue turns yellow
(d)  methyl orange turns red

1)       bitter taste
2)       slippery and soapy to the touch
3)       a good conductor of electricity in solution
4)       reacts with an acid to produce a salt and water
5)       Indicators:
(a)  red litmus turns blue
(b)  colourless phenolphthalein turns pink
(c)  neutral (green) bromthymol blue turns blue
(d)  methyl orange turns yellowish orange

author avatar
William Anderson (Schoolworkhelper Editorial Team)
William completed his Bachelor of Science and Master of Arts in 2013. He current serves as a lecturer, tutor and freelance writer. In his spare time, he enjoys reading, walking his dog and parasailing. Article last reviewed: 2022 | St. Rosemary Institution © 2010-2024 | Creative Commons 4.0

Leave a Reply

Your email address will not be published. Required fields are marked *

Post comment