equilibria 5.6

a reaction that can go backwards as well as forward ⇌

amount of reactants and products and the conditions (such as temperature and pressure)

enthalpy change for a reversible reaction always refers to the forwards reaction for the backwards reaction, enthalpy change is the same number but the opposite sign for example: in the reaction in which enthalpy change is +113 kJ/mol +113kJ/mol = forward reaction -113kJ/mol = backwards reaction

CuSO4 5H2O ⇌ CuSO4 + 5H2O to make reaction go forward you heat hydrated copper sulphate crystals = blue to white as they evaporate all their water to make the reaction go backwards you add water to anhydrous copper sulphate = the white powder absorbs the water and turns blue in the process

NH4Cl(s) ⇌ NH3(g) + HCl (g) to make the reaction go forward you heat to make the reaction go backwards you allow NH3 and HCl to mix in the absence of heat = white NH4Cl forms immediately wherever the cold gases meet

when a reversible reaction is left in a sealed container, this results in the forward and backwards reactions eventually balancing out therefore the mixture of reactants and products in the container is referred to as being in dynamic equilibrium

dynamic = the forward and backwards reactions are still happening just as the same rate equilibrium = the concentration of reactants and products remain unchanged

the resulting balance of products and reactants in an equilibrium mixture is called the equilibrium position

• amount of reactants or products • gas pressure • temperature

in whichever direction uses it up shift to remove the extra you added

in whichever direction creates it shift to create more of it

to whichever side has the fewest moles of gas

to whichever side has the most moles of gas

in whichever direction is endothermic

in whichever direction is exothermic

they balance as catalysts increase the rates of both forward and backward reactions therefore having no effect on the position of equilibrium