# Rates of Reaction

##### 7.2 Suggest practical methods for determining the rate of a given reaction
• Rates of reactions can be measured using the amount of product used, or amount of product formed over time:

Rate of reaction = amount of reactant used

Time

Rate of reaction = amount of product formed

Time

• Quantity of reactant or product can be measured by the mass in grams or by a volume in cm^3
• Units of rate of reaction may be given as g/s or cm^3/s
• (HT only) use quantity of reactants in terms of moles and therefore, units for rate of reaction in mol/s
##### 7.3 Explain how reactions occur when particles collide and that rates of reaction are increased when the frequency and/or energy of collisions is increased
• Chemical reactions only occur when the reacting particles collide with enough energy, the minimum amount of energy required is called the activation energy.
##### 7.4 Explain the effects on rates of reaction of changes in temperature, concentration, surface area to volume ratio of a solid and pressure (on reactions involving gases) in terms of frequency and/or energy of collisions between particles
• Increasing the temperature increases the rate of reaction. As increasing temperature increases the speed of the moving particles, so they collide more frequently and energetically.
• Increasing pressure in reacting gases increases the rate of reaction, as it increases the frequency of collisions.
• Increasing concentration of reacting solutions increases the rate of reaction, as it increases the frequency of collisions.
• Increasing the surface area of solid reactants increases the rate of reaction, as it increases the frequency of collisions.
##### 7.5 Interpret graphs of mass, volume or concentration of reactant or product against time
• To find the rate of reaction graphically
• Draw tangents to curves and use the slope of the tangent as a measure of the rate of reaction
• (HT only) calculate the gradient of a tangent to the curve on these graphs as a measure of rate of reaction at a specific time
• Gradient = rate of reaction, therefore use this information to interpret any given graph, therefore a steeper line means a greater increase/decrease in rate
##### 7.6 Describe a catalyst as a substance that speeds up the rate of a reaction without altering the products of the reaction, being itself unchanged chemically and in mass at the end of the reaction
• Catalysts are substances that speed up chemical reactions without being changed or used up during the reaction.
##### 7.7 Explain how the addition of a catalyst increases the rate of a reaction in terms of activation energy

• Catalysts decrease the activation energy; this increases the proportion of particles with energy to react.
• Catalysts provide a different pathway for a chemical reaction that has a lower activation energy.
##### 7.8 Recall that enzymes are biological catalysts and that enzymes are used in the production of alcoholic drinks
• Enzymes act as catalysts in biological systems
• Yeast is the enzyme used in the production of ethanol as it is fermented, ethanol is in alcoholic drinks
##### 7.8 Recall that enzymes are biological catalysts and that enzymes are used in the production of alcoholic drinks
• Enzymes act as catalysts in biological systems
• Yeast is the enzyme used in the production of ethanol as it is fermented, ethanol is in alcoholic drinks