Topic 6a : Rates of Reaction

What is a rate of a chemical reaction ?

how fast the reactants are changed into products

Name 3 examples of reactions going from pretty slow to really fast ?

1. the rusting of iron (pretty slow)

2. A metal (e.g. magnesium) reacting with an acid to produce a gentle stream of bubbles (moderate speed)

3. An explosion (really fast)

what 4 main conditions affect the rate of reaction ?

1. Temperature — the higher the temperature, the faster the reaction

2. Concentration (or pressure for gases) - the more concentrated the reactants (or the higher the pressure), the faster the reaction

3. Surface area (depends on the size of solid pieces) — the larger the surface area (the smaller the pieces), the faster the reaction

4. Catalysts — the more catalysts present , the faster the reaction

As stated in Collision Theory what 2 factors affect the rate of reaction ?

1. The collision frequency of reacting particles (how often they collide).The more there are in a certain amount of time, the faster the reaction is.

   • as collision frequency increases , the probability for successful collisions increases

2. The energy transferred during a collision. Particles have to collide with enough energy to be successful.

   • as the energy of collisions increase , the more collisions are successful

what is activation energy ?

the minimum amount of energy that particles must have in order to react

Which of the prementioned conditions affect the frequency of collisions ? (3)

1. (Increase in) Temperature -

   • temperature increases

   • particles move quicker

   • particles collide more often

   • more frequent collision means faster rate of reaction

2. (Increase in) Concentration/Pressure (for gasses) -

   • solution is made more concentrated

   • there are more particles of reactants colliding between the water molecules

   • collisions of the particles of reactants are more likely

   • more frequent collisions means faster rate of reaction

3. (Increase in) Surface area to volume ration -

   • the surface area : volume of a solid increases when your break into smaller bodies

   • for the same volume of solid , the particles surrounding

   • it in the solution have a larger surface area to work on

   • more frequent collisions means faster rate of reaction

Which of the prementioned conditions affect the energy of collisions ? (1)

1. (Increase in) Temperature -

   • increase in temperature

   • increase in speed of particles as they collide (increase in energy of collision)

   • there are more particles colliding with enough energy to react successfully

2. Catalysts

   • they decrease the activation energy needed for the reaction to occur by providing an alternative reaction pathway with a lower activation energy

what is a Catalyst ?

A catalyst is a substance which can speed up a reaction without being changed or used up in the reaction

what is an Enzyme ?

A biological catalyst that works similarly to all other catalysts but will generally only catalyse a certain reaction for a specific molecule