#FactorsAffectingRateOfReactions

#Chemistry

#ChemicalReactions

Introduction

• For a reaction to occur, the particles that are reacting must collide with each other. Only some of all the collisions that take place cause a chemical change to happen. These are called 'successful' collisions. The greater the number of 'successful' collisions, the faster the rate of a reaction. This is called the 'collision theory'.

• There are four factors that affect the rate (speed) of a chemical reaction:

  • Temperature

  • Concentration

  • Particle Size

  • Use of Catalyst

Temperature

• If the temperature is increased, the particles have more energy and so move quicker. Increasing the temperature increases the rate of reaction because the particles collide more often and with more energy. The higher the temperature, the faster the rate of a reaction will be.

Concentration

• If the concentration of reactants is increased, there are more reactant particles moving together. There will be more collisions and so the reaction rate is increased. The higher the concentration of reactants, the faster the rate of a reaction will be.

Particle Size

• By decreasing the particle size of a reactant, we are increasing its surface area. The greater the surface area, the higher the chance of collisions, thus the faster the rate of reaction. The smaller the particle size the faster the reaction.

Use of Catalyst

• A catalyst increases the rate of a reaction but it is not used up in the reaction. If a catalyst is present, the reacting particles can collide more successfully with less energy and so the reaction can take place at a lower temperature.

Monitoring

• The rate of a chemical reaction is a measure of how fast the reactants are being used up and how fast the products are being made.

• The rate can be determined by measuring:

  • changes in the concentration of the reactants or products

  • changes in the mass of the reactants or products

  • changes in the volume of the reactants or products

• For example, when dilute hydrochloric acid reacts with zinc metal, zinc chloride and hydrogen gas are produced.

• There are two simple ways to measure the rate of this reaction in the lab.

• 1. If the reaction is set up on a balance as shown, the mass of the apparatus can be monitored throughout the reaction. As hydrogen bubbles escape, the apparatus will lose mass.

• 2. An alternative way to monitor the reaction is by collecting and measuring the volume of the gas as it is produced. The gas can be collected in a gas syringe or over water (as long as it is insoluble in water).

Calculating

• Using the results of experiments like these, the average rate of the reaction can be calculated. No matter which quantity is measured during the course of a reaction, the average rate of reaction can be calculated using the equation below.

• Average Rate = Change in Measurable Quantities (Volume, Mass or Concentration) / Change in Time.