Unit 1: Section 5 - Kinetics, Equilibria and Redox Reactions

Reaction rate = Amount of reactant used or product formed / Time

A reaction between 2 particles won’t take place unless they collide in the correct orientation and with at least the minimum amount of kinetic energy required

The minimum amount of kinetic energy that particles need to react

The area under the graph - the total number of molecules The curve starts at (0,0) - no molecules have zero energy The peak - the most probable energy To the right of the peak - mean energy of all the molecules Molecules that can react - to the right of the activation energy

• If you increase the temperature of a reaction, the particles will on average have more kinetic energy and will move faster therefore the rate of reaction will be faster • A greater number of particles will have at least the activation energy and be able to react • This pushes the Maxwell-Boltzmann to the right, but there are the same number of particles so the area has to stay the same • As the molecules are moving faster, they will also collide faster • As you get 2 effects happening, small increases in temperature will lead to large increases in reaction rate

• The particles will on average be closer together • If they’re closer, they will collide more often • If collisions happen more frequently, they’ll have more chances to react • Therefore the rate of reaction increases

• More of the gas particles are closer together • So they are more likely to collide so collisions take place more frequently • Therefore the reaction rate increases

A substance that increases the rate of a reaction by providing an alternative pathway with a lower activation energy, the catalyst is chemically unchanged at the end of the reaction

• Provide an alternative reaction route of lower activation energy • More particles have energy > activation energy, so more frequent successful collisions, so increased reaction rate

• In an energy profile, the activation energy will be lowered • In a Maxwell-Boltzmann distribution curve, the activation energy line is shifted the the left

• Used when the product is a precipitate which clouds the solution • Watch a cross through the solution and time how long it takes to disappear • You need to have the same observer every time, and the same cross because roughly the same amount of precipitate will be produced when the cross is obscured • This is a very subjective method though

• Used when the product is a gas • As gas is produced, the mass of the reaction mixture decreases • The method is accurate, but as releases gas into the atmosphere, it is usually done in a fume cupboard

• Use a gas syringe to measure the volume of gas being produced • Gas syringe usually gives the volume to the nearest 0.1cm^3 so is usually an accurate method

When the forward reaction is going at the same rate as the backward reaction so the concentrations of reactants and products stays constant This can only happen in a closed system

If a reaction at equilibrium is subjected to a change in concentration, pressure or temperature, the position of equilibrium will move to counteract the change

• If you increase the concentration of a reactant, the equilibrium will shift to the right to make more product • If you increase the concentration of a product, the equilibrium will shift to the left to make more reactant • Decreasing the concentration will have the opposite effect

• Increasing the pressure will shift the equilibrium to the side with fewer gas molecules, this will reduce the pressure • Decreasing the pressure will shift the equilibrium to the side with more gas molecules, this will increase the pressure

• If you increase the temperature, the equilibrium position will shift in the endothermic direction • If you decrease the temperature, the equilibrium position will shift in the exothermic direction

Catalysts have no effect on the position of the equilibrium, they can’t increase yield but they do mean equilibrium is reached faster

The equilibrium constant which can be used to find concentrations in equilibrium mixtures

• If you change the temperature of the system, you also will change the equilibrium concentrations of the products and reactants so Kc will change - if change in temp=more product=Kc rises but if change in temp=less product=Kc decreases • Changing concentrations or adding a catalyst doesn’t affect Kc

A reaction where electrons are transferred

The loss of electrons OR Gain of oxygen (or any electronegative element) OR Loss of hydrogen (or any electropositive element)

The gain of electrons OR Loss of oxygen (or any electronegatice element) OR Gain of hydrogen (or any electropositive element)