4 c) Rates of reaction Flashcards
4.17 describe experiments to investigate the effects of changes in surface area of a solid, concentration of solutions, temperature and the use of a catalyst on the rate of a reaction
http://www.shawonnotes.com/index/section_4_physical_chemistry_igcse_chemistry/0-35
4.18 describe the effects of changes in surface area of a solid, concentration of solutions, pressure of gases, temperature and the use of a catalyst on the rate of a reaction
Temperature: The higher the temperature, the faster the rate of reaction.
Concentration: The more concentrated the substance used, the faster the speed of a chemical reaction.
Pressure: The speed of reactions which involve gases is faster at higher pressures.
Particle Size: Smaller particles like powders have a much greater surface area than larger lumps or crystals. Within a greater surface area, the other reactant can attack it more easily and thereby increase the speed of reaction.
4.19 understand the term activation energy and represent it on a reaction profile
Activation energy is the minimum energy that molecules must possess during their collisions in order for a chemical reaction to occur.
http://shawonnotes.ucoz.com/IGCSE_Chemistry/images/clip_image102.jpg
4.20 explain the effects of changes in surface area of a solid, concentration of solutions, pressure of gases and temperature on the rate of a reaction in terms of particle collision theory
Temperature: When the temperature is raised, the reactant particles have a greater heat energy, causing them to move about more and with a greater kinetic energy. They, therefore, stand a better chance of colliding into another reactant molecule with sufficient energy to convert into product molecules.
Concentration: When concentrated substance is used, there is a greater likelihood that reacting molecules will collide with one another with sufficient energy to form products.
Pressure: In higher pressure the concentration within a certain volume increases, therefore more collision occurs.
Particles Size: Smaller pieces have large surface area and therefore more collisions.
4.21 explain that a catalyst speeds up a reaction by providing an alternative pathway with lower activation energy.
A catalyst is a substance which increases the rate of chemical reaction, without itself being chemically changed at the end of the reaction.
Catalysts work by proving a more direct route from reactants to products. If we plot energy against time for a reaction, there is an energy barrier over which the reactants have to pass. The height of this barrier above the energy of the reactants is called the activation energy. What catalysts do, is to lower this activation energy, so as to allow the reactants to change into products more quickly.
