Rates of Reactions :: GCSE Chemistry Coursework Investigation

Rates of Reactions Aim: I am going to investigate how the rate of the reaction between sodium thiosulphate and hydrochloric acid depends on the concentration of sodium thiosulphate. The reaction rate of a chemical reaction is the speed of production of products from reactants. Sodium thiosulphate + hydrochloric acid ==> sodium chloride + sulphur dioxide + water + sulphur Na2S2O3 (aq) + 2HCl (aq) ==> 2NaCl (aq) + SO2 (aq) + H2O (l) + S(s) The solid sulphur (S(s)) formed in this reaction makes the colourless solution go cloudy. Factors: The factors I believe that will affect what happens in the investigation are: * Catalyst- A catalyst s a substance which alters the rate of a chemical reaction but is chemically unchanged at the end of the reaction. - A catalyst speeds up a reaction; an inhibitor (a substance) slows it down. * Concentration- The more concentrated the faster the rate (note in some cases the rate may be unaffected by the concentration of a particular reactant provided it is present at a minimum concentration). Remember for gasses, increasing the pressure simply increases the concentration so that's the same thing. * Surface area- greater surface area and since the reaction occurs at the surface we get a faster rate. * Temperature- Usually reactions speed up with increasing temperature ("100C rise doubles rate"). The collision theory: Particles need to collide with each other to react and the collision theory is all about this. The can be affected by the temperature of the particles, the concentration of the particles, whether a catalyst is used or the surface area (if the particles are solid). Temperature affects the rate of a reaction because if particles are cold, they move slowly and there are few collisions between them. But when they are heated up they move much faster or you can also say they have more kinetic energy. When the move faster there is more of a chance of a collision. More collisions means that the reaction goes faster - its rate increases. Concentration of the acid used also affects the rate because when there is a higher concentration (more acid) there are more particles to collide with each other-more collisions means that the reaction goes faster. A catalyst is a substance that can speed up a chemical reaction without actually being used up in the reaction. It gives the particles a surface to stick to so they can collide with each other there - more collisions. Again when there are more collisions this causes the reaction to go faster. Surface area also affects the rate of a reaction if the particles are