Collision Theory - 4th
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when can a chemical reaction only happen?
• if the reactant particles collide with enough energy
what is activation energy?
• the amount of energy the particles need to react is called activation energy
what will happen to particles which collide with less energy than the activation energy?
• will just rebound and remain unchanged
what does the overall rate of reaction involving millions of particles depend on?
• collision frequency • percentage success
what is collision frequency?
• how often do the particles collide with each other
what is percentage success?
• what percentage of the collisions have enough energy?
what are four common factors which affect rate of reaction?
• surface area • concentration • temperature • catalysts
why does a higher solid surface area increase the rate of reaction?
• more of the solid is exposed to the other particles • so the collision frequency is higher • so there are more successful collision per unit time
why does a higher temperature a increase the rate of reaction?
• the particles have more kinetic energy • so the percentage of collisions with enough energy is higher • so there are more successful collisions per unit time
why does a higher solution concentration/gas pressure increase the rate of reaction?
• there are more particles per unit volume • so the collision frequency is higher • so there are more successful collisions per unit time
why does a catalyst increase the rate of reaction?
• they provide an alternative route with a lower activation energy • so the percentage of collisions with enough energy is higher • so there are more successful collisions per unit time
how can you increase the concentration of a solution/gases?
• by dissolving more solute particles
how can you increase the pressure of a solution/gases?
• by making the reaction vessel smaller
how can the effect of concentration on rate be demonstrated?
• by reacting sodium thiosulphate solution with hydrochloric acid to make sodium chloride, sulphur solid , sulphur dioxide and water
what is the chemical equation for the disappearing cross experiment?
• Na2S2O3 (aq) + 2HCl (aq) -> 2NaCl (aq) + S (s) + SO2 (g) + H20
describe the observations of the disappearing cross experiment?
• in this reaction, a solid (sulphur) is slowly produced • after a while, you cannot see through the mixture any longer • this is measured by observing a black cross under the mixture
what are the variables for the disappearing cross experiment?
• input : the concentration of the Na2S2O3 (aq) • output : the time taken for the cross to disappear • control : total volume of solution, concentration of HCl (aq), temperature
how is rate calculated?
• rate (s^-1) = 1/time taken (s)
what is the relationship between rate and concentration?
• they are proportional
how is surface area increased?
• by cutting or grinding up the solid
how is the effect of surface area on rate demonstrated?
• by reacting calcium carbonate marble chips with hydrochloric acid to form calcium chloride, water and carbon dioxide gas
what is the chemical equation for the marble chip experiment?
• CaCO3 (s) + 2HCl (aq) -> CaCl2 (aq) + H2O (l) + CO2 (g)
what are the variables in the marble chip experiment?
• input : the sizes of the CaCO3 (s) chips • output: the volume of CO2 (g) • control: the mass of CaCO3(s), the volume and concentration of HCl (aq), temperature
how is the volume of carbon dioxide measured in the marble chip experiment?
• using a gas syringe or inverted measuring cylinder in water