7-Rates of Reaction and Energy Changes

Activation Energy

The minimum amount of energy that particles must collide with to react.

Catalyst

Increases the rate of reaction by providing a different pathway for the reaction that has a lower activation energy. They are not used up in reactions.

Collision Theory

Chemical reactions only occur when colliding particles collide with the correct orientation and sufficient energy.

Displacement

A chemical reaction in which a more reactive element displaces a less reactive element from its compound.

Effect of Concentration on Reaction Rate

Increasing the concentration of reactants in solution means the reacting particles will be closer together. This means they will collide more often so there will be a higher rate of sucessful collisions and a faster rate of reaction.

Effect of Pressure on Reaction Rate

Increasing pressure of gaseous material means the reacting particles will be closer together. They woll collide more often so there will be a higher rate of sucessful collisions and a fater rate of reaction.

Effect of Surface Area on Reaction Rate

Increasing the surface area of the reactants means there are more exposed reacting particles. This means more frequent successful collisions so rate of reaction increases.

Effect on Temperature on Reaction Rate

Increasing the tmeperature means the particles will have more kinetic energy and so will move faster. If the molecules are moving faster they will collide more often and, science they’ve gained kinetic energy, a larger proportion of the particles will have at least the activation energy. For both these reasons the rate of reaction increases.

Enzymes

Biological catalysts which speed up biochemical reactions so that organisms can survive. Used in production of alcoholic drinks.

Endothermic Reaction

A reaction that takes in energy from the surroundings so the temperature of the surroundings decreases. In an endothermic reaction, the energy needed to break existing bonds is greater than the enrgy released from forming new bonds.

Exothermic Reaction

A reaction that transfers energy to the surroundings so the temperature of the surroundings decreases. In an enxothermic reaction, the energy released from forming the new bonds is greater than the energy needed to break exisiting bonds.

Neutralisation

The reaction in which an acid and a base react to form salt and water.

Overall Energy of the Reaction

The difference between the sum of energy needed to break bonds in the reactants and the sum of energy released when the bonds in the products are formed.

Precipitation Reaction

A reaction in which solutions react to form an insoluble product.

Rate of Reaction

The measure of the amount of product formed or reactant used over time. The units of rate of reaction may be given as g/s, cm³ or mol/s.

Reaction Profile

Graphs used to show the relative energies of reactants and products, the activation energy and the overall energy change of a reaction.