Equilibrium

• Open Chemical System - allows matter and energy to be exchanged with surroundings
• Closed chemical system - exchanges energy but not matter with surroundings
• Dynamic Equilibrium is the state reached when the amount of reactants and products remain constant even though forward and reverse reactions are still occurring
• Dynamic Equilibrium is characterised by the concentration of all species being constant, the rate of both reactions being equal, occurring in closed system with a constant temp and macroscopic properties don't change
• Macroscopic properties are properties that can be seen with the naked eye, such as colour, phase(solid, liquid, gas), pressure, temperature and density
• For water, equilibrium is reached when the rate of evaporation is equal to the rate of condensation
• Le Chateliers principle states "If a system at equilibrium is subjected to a change in conditions, it will adjust to re-establish equilibrium in such a way as to partially counteract the imposed change"
• Factors that affect Equilibrium are concentration (of reactants or products), dilution, volume/pressure of a gaseous system and temperature
• If there is an increase in concentration, the system shifts in the opposite reaction to reduce it. Eg. If OH- (reactant) is increased suddenly, increased frequency of collisions between reactants, the forward reaction will increase relative to the reverse reaction and equilibrium shifts to the right
• If a product's concentration is increased, increased frequency of collisions between products, the rate of the reverse reaction will increase relative to the forward reaction and equilibrium shifts to the left
• Graphs use mole ratios to decide how much a species increases or decreases. If it is in a 1(reactant):2(reactant):2(product) ratio, and a reactant is added, the first reactant decreases half as much as the second. The product will increase as much as the second reactant falls
• If you add more of a solid to a chemical reaction already at equilibrium, there will be no effect. Solids have a fixed concentration that cannot be changed
• Adding water to a system/diluting it will decrease the initial concentration of ALL species. The system will favour the reaction with the most ion moles (does not include solids or liquids)
• If the ion mole ratio is the same, the rate of the forward and reverse reaction will be the same and neither side will be favoured, producing no colour change
• Full marks: State what caused the change, which reaction is favoured, why it is favoured, rate increases relative to the other, frequency of collisions increases between reactants/products (collide with sufficient energy), increase in concentration of the reactants/products
• An increase in pressure results in particles being closer together, increasing frequency of collisions with sufficient energy, speeding up the reaction
• An increase in concentration increases the amount of particles in a given volume, increasing the frequency of collisions with sufficient energy, speeding up the reaction
• A change in pressure only affects GASES. When the pressure of a system is changed, concentration of all species are changed. For equilibrium, it is dependent on the moles of gases
• An increase in pressure (decreased volume) causes a relative increase in the rate of reaction to the side with the LEAST number of moles of gas
• A decrease in pressure (increased volume) causes a relative increase in the rate of reaction to the side with the MOST number of moles of gas
• Increased system pressure where reactants have more moles: an increased frequency of collisions between reactants, sudden increase in all gases, ratio of 3:2, reaction favours the side with the least number of moles, the rate of the forward reaction increases relative to the rate of the reverse, equilibrium shifts to the right
• When volume is doubled, concentration of gases are halved. Using ratios, certain species will fall/increase relative to each other
• Partial Pressure is the pressure that would be exerted by one of the gases in a mixture if it occupied the same volume on its own
• Changing the partial pressure of one reaction species will cause the same effect as concentration
• Exothermic reactions release heat, their enthalpy is negative, and heat is with the products
• Endothermic reactions take in heat, have a positive enthalpy (Ando/Endo), and the heat is with the reactants
• Increasing temperature causes the system to favour the reaction that will remove heat (the endothermic reaction is favoured and therefore that reaction rate will increase relative to the other)
• Decreasing temperature causes the system to favour the reaction that will increase heat (the exothermic reaction is favoured and therefore that reaction rate will increase relative to the other)
• If the temperature is increased, in a reaction where the forward reaction is exothermic (state this fact), the system favours the reverse reaction which is endothermic, there is an increased frequency of collisions between products, the rate of the reverse reaction increases relative to the forward reaction and the equilibrium shifts to the left
• If the concentration or partial pressure is what is measured in a graph, there will be a sudden increase or decrease by one species. If it is temperature, there will be gradual changes of all species. If its system pressure, sudden increase/decrease of all species
• A catalyst has no effect on concentrations at equilibrium as it lowers the activation energy for both reactions equally. If a catalyst is added to a system not at equilibrium, the system will reach equilibrium quicker due to a lowered activation energy and increased reaction rates
• Equilibrium constant expressions: Kc = [C][D] / [A][B] where C and D are the product concentrations and A and B are the reactant concentrations. Each are raised to the power of the moles they have. 2NO3 = [NO3]^2
• Equilibrium constant/law expressions are only for gases and aqueous solutions as solids and liquids have a fixed concentration and do not change
• Equilibrium constants predict the relative concentrations of products and reactants and therefore the position of the equilibrium. If the constant is large, there are more products (higher concentration), the reaction goes towards completion and the equilibrium lies to the right. If the constant is small, there are more reactants (higher concentration), the reaction is insignificant, and equilibrium lies to the left. If it is close to 1, significant concentrations of all species are present
• Ocean acidification is the process where the ocean acts as a carbon sink and absorbs 1/3 of the CO2 generated. As CO2 levels rise, more dissolves and equilibrium shifts to the right. This also means more carbonic acid is produced (increasing ocean acidity), the increase in H+ and decrease in CO3- affect organism that rely on calcification and kill them as their shells decompose
• Calcification is a process which results in the formation of calcium carbonate structures