GCSE EDEXCEL CHEMISTRY UNIT 7 - RATES OF REACTION AND ENERGY CHANGES

Core practical: Investigate the effects of changing the conditions of a reaction on the rates of chemical reactions by: measuring the production of a gas (in the reaction between hydrochloric acid and marble chips) and observing a colour change (in the reaction between sodium thiosulfate and hydrochloric acid)

In these experiments, you are inverstogating the effect on rate of changing the size of marble chips.
(Smaller chips \= larger surface area \= faster rate)
• also the effect of changing the concentration of hydrochloric acid (greater concentration \= greater number of particles in a given volume \= faster rate)

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
•The quantity of reactant or product can be measured by the mass (g) or by the volume (cm3)
• Units of rate of reaction may be given as g/s or cm3/s

•to measure reactant used : if the product is a gas,which will be given off, you can carry out the reaction on a set of weighing scales and measure how much mass is lost (cover with cotton wool so nothing can escape)

To measure how much product is formed : If the product is a gas, you can measure the volume of gas produced in a gas syringe

Explain how reactions occur when particles collide

Chemical reactions occur when the reacting particles collide with enough energy, the minimum energy needed for a reaction to occur is called the activation energy

What happens to the rate of reaction when the frequency and/or energy of collisions is increased

The rate of reaction increases, as more particles can reach their activation energy

Which factors can you alter to increase the rate of a reaction

1) Increasing temperature
2) Increasing pressure
3) Increasing concentration
4) Increasing surface area
5) Using a catalyst

Explain the effects on rates of reaction of changes in temperature, concentration, surface area : volume ratio (and pressure on reactions involving gases) in terms of frequency and/ or energy of collisions between particles

•Increasing temperature - increases the rate of reaction because it increases the kinetic energy of particles so they collide more frequently and successfully

•Increasing pressure - increases the rate of reaction as it increases the number of particles in a given volume, so successful collisions are more frequent

•Increasing concentration- Increases the rate of reaction as it increases the number of particles in a given volume and so increases the frequency of successful collisions

•Increasing the surface area - Particles are closer together, so there are more frequent successful collisions

Interpret graphs of mass, volume or concentration of a reactant or product against time

•Draw tangents to curves, using the slope as a measure of the rate of reaction
•The gradient \= rate of reaction

Describe a catalyst (in terms of rate of reaction)

Catalysts are substances that speed up the rate of reactions without altering the products of the reaction, being itself unchanged chemically and in mass at the end of the reaction

Explain how the adding a catalyst increases the rate of reaction in terms of activation energy

Catalysts decrease the activation energy by providing an alternative pathway for a chemical reaction that has a Lower activation energy. Therefore the amount of particles that are able to react in a given volume increases, so there are more successful and frequent collisions , which increases the rate of reaction

What are enzymes and how are they used in the production of alcoholic drinks

Enzymes act as biological catalysts that speed up the rate of reaction without being used up in the reaction.

Yeast is the enzyme used in the production of ethanol as it is fermented from sugars, ethanol is in alcoholic drinks