Rates of Reaction

• mean rate of reaction= quantity of product formed/ time taken
• if a tangent has a steeper slope earlier in the reaction compared to later in the reaction this shows that the reaction Is faster at the start than toward the end.
• Rate = y/x
• Chemical reactions can only take place when the reacting particles collide with each other, the collisions must have sufficient energy.
• Rate of a chemical reaction is determined by the frequency of successful collisions.
• Frequency = number of successful Collisions per second
• Reactions are rapid initially because there are a large number of reactant molecules
• Over time reactions slow down because the number of reactant molecules is running out
• The reaction stops because all of the reactant molecules have run out
• the rate increases if we increase the concentration, the rate is proportional to the concentration.
• The higher concentration is a faster reaction
• With a higher concentration you get more product at the end because we started with more reactant molecules at the start
• Because we have more collisions per second the rate increases when we increase the surface area of a solid reactant
• Smaller sized blocks of solid reactant have a greater surface area to volume ratio than larger blocks. this means that they have more particles on the surface so there are more collisions per second this increases the rate of reaction.
• Activation energy = minimum amount of energy that the particles must have in order to react
• Increasing the temperature increases the rate of chemical reactions
• Increasing the temperature increases the energy of the particles
• if particles have more energy they move faster, this increases the frequency of collisions therefore there is a greater number of collisions per second
• catalysts Increase the rate of chemical reactions but are not used up during the reaction
• Catalysts allow us to carry out reactions quickly without needing to increase the temperature, this saves money.
• Because catalysts are not used up during the reaction, we can reuse them again
• Rate of reaction depends on the number of particles that have enough energy to cross the activation energy barrier and collide successfully
• Catalysts increase the rate by providing a different pathway for reaction that has A lower activation energy
• When a catalyst is present the particles require less energy to cross the activation energy barrier which means more particles can successfully collide per second
• We do not include catalysts in the chemical equation for a reaction that is because they are not used up in the reaction.
• Different reactions need different catalysts
• Enzymes act as catalysts for living organisms
• If a reversible reaction is exothermic in one direction, it is endothermic in the opposite direction.
• The same amount of energy is transferred
• Equilibrium = the forward and reverse reactions will take place at exactly the same rate
• If a system is at equilibrium and a change is made to the conditions then the system responds to counteract the change
• At equilibrium the system will counteract any changes that we make
• If we change the concentration of the reactant or products then the system is no longer at equilibrium
• The concentrations of all the substances will change until equilibrium is reached
• If we decrease or increase the concentration the system is no longer at equilibrium. then more reactants will react to form the produce until equilibrium is reached again
• when the exothermic reaction takes place, energy is released and the temperature of the system increases
• In an endothermic reaction energy is taken in and the temperature of the system decreases
• If we increase the temperature of a system the equilibrium shifts to the left to reduce the temperature
• if we decrease the temperature of a system equilibrium shifts to the right to increase the temperature
• Pressure affects reactions involving gases