Chemistry


Collision Theory

The collision theory is the concept that particles must collide with sufficient energy in order for a chemical reaction to take place. The rate of reaction depends on the frequency (how often) of the collisions.

For a chemical reaction to occur the collisions need:

  • sufficient energy

  • orientation of particles

Factors which increase rate of reaction must relate to one of the following:

  • frequency of collision (more = faster)

  • effective collisions (occurring with sufficient energy)

  • effective collisions (orientation)


Practice questions:


How are reaction rate and collision theory related to each other? Use collision theory to answer your question

Reaction rate and collision theory are closely related as collision theory explains that for a reaction to occur, reactant molecules must collide with sufficient energy and proper orientation. The reaction rate depends on the frequency and effectiveness of these collisions. Factors such as higher reactant concentrations, increased temperatures, presence of catalysts, and greater surface area enhance the frequency or effectiveness of collisions, thereby increasing the reaction rate.

How does surface area/ concentration/ temperature effect the rate of reaction?

Surface area:

If there is a greater surface area available for a reactant to access, this increases the chances of a collision to occur. Therefore since the frequency of these collisions are increased, the rate of reaction will also increase in speed.


Concentration:

If there is a greater concentration, then there are more reactant particles moving around. This therefore increases chances of collisions to occur between the particles, therefore speeding up the rate of reaction in the experiment.


Temperature:

If there is a higher temperature than the average speed and kinetic energy of the reactant molecules are increased. This increases the chance of collisions because as more molecules move faster, the number of molecules with sufficient energy increases, resulting in a faster formation of products.


What is activation energy?

Activation energy is the energy required to break the intramolecular forces between the bonds of the reactants in order to cause a reaction.

The higher the activation energy, the more energy required for a reaction to take place. This is because if the energy required to break the intramolecular forces of the reactants is higher than the energy of the collisions taking place, than the energy is not enough to cause a reaction and break the barriers of the reactant.

Lower activation energy would proceed faster as a lower amount of energy is needed to break the intramolecular forces between the reactants.


Catalysts

A substance which speeds up a reaction without being chemically altered. When a reaction is finished, you will have the same amount as you had in the beginning

Catalysts work by lowering the activation energy required for a reaction to occur


what is a Systematic error

a consistent error which affects the results

  • constant in magnitude

  • usually due to observer, instrument or environmental conditions

  • e.g. debris left in a test tube causing mass to be 0.1 g more than it should

How to prevent:

  • use calibrated equipment

what is a random error

inconsistent error

  • e.g reaction time to starting a timer

How to prevent:

  • perform experiment multiple times

  • discard outliers

  • average results


Accuracy (systematic errors)

accuracy is how close the results of an experiment is to its true theoretical value

improve by:

  • minimising systematic errors (e.g. zeroing scales)

  • use better equipment

    • more sensitive/smaller increment scale (mm is more accurate than cm)

Reliability (random errors)

Reliability is the consistency of an experiment and whether or not it can be replicated with the same results.

improve by:

  • minimising random errors

  • having controlled variables

  • discard outliers, average results


Temperature

Temperature is a measure of the average kinetic energy of the atoms or molecules in the system

Heat

Heat is the transfer of thermal energy between two bodies at different temperatures. hotter transfers to colder