Equilibrium and rate

• Kp is the equilibrium constant for pressures.
• Within a gaseous system, each gas has a partial pressure which adds up to give the total system pressure.
• Molar fraction is the moles of the substance being measured divided by the total moles in the system.
• The partial pressure of a substance equals the molar fraction multiplied by the total pressure.
• Kp equals the product of the partial pressures of the products divided by the product of the partial pressures of the reactants. Each partial pressure is raised to a power equal to the number of moles of that specific substance in the reaction equation.
• In a reaction system, one reaction will be endothermic and the opposite will be exothermic.
• Reversible reactions will reach dynamic equilibrium where the rate of reaction of the forwards and backwards reaction is the same and remains at a constant rate.
• Le Chatelier's principle describes how the equilibrium mixture will change if the reaction conditions are altered and states that the system will alter to oppose any change it is subjected to.
• If the temperature of a reversible reaction is increased, the endothermic reaction is favoured, if pressure is increased the side of the reaction with fewest moles is favoured and if concentration is increased the side producing the other products is favoured, and visa versa for all.
• Kc is the equilibrium constant for concentrations.
• The equation for Kc is the concentrations of the products to the power of their individual mole ratio divided by the concentration of reactants to the power of their individual mole ratio.
• The value of Kc is not affected by overall concentration change or the use of a catalyst, but is affected by temperature.
• The rate of reaction shows how fast reactants are converted into products. It depends on the concentrations of the reactants and a rate constant, k.
• The order of the reaction with respect to a species shows how much affect a species has on the rate of reaction compared to the other species, with the total order being the sum of separate orders.
• The concentration of a zero order species has no effect on the rate of reaction, the concentration of a first order species is directly proportional to the rate, and the concentration squared of a second order species is proportional to the rate.
• Rate is the rate constant multiplied by the concentrations of the reactants to the power of their order.
• The Arrhenius equation shows how the rate constant and temperature are related exponentially: k = A e ^ - (E / R x T), where A is the pre-exponential factor, E is the activation energy, R is the gas constant and T is the temperature in kelvin.
• The overall rate is determined by the slowest step of the reaction, and therefore rate equations include the species involved in the stages up to and including the rate determining step.
• Rate equations can be determined experimentally by plotting the concentration of a reaction over time and then rate is found by drawing a tangent at t = 0 as this is the only time the exact concentration is known. This is repeated at varying concentrations to get a graph of rate against concentration.