# Equilibria -4

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• Created by: Shannon
• Created on: 02-04-15 15:02
• Equilibria
• Dynamic equilibria
• The rate of forward and backward reactions are equal
• No further changes in concentration
• Occurs in a close system
• General rules
• Heat favours the endothermic direction
• Increasing pressure will shift equilibrium to the side with the fewest particles
• On the addition of a reactant or product, equilibrium will shift in the direction that will reduce its effects and conversely
• Equilibrium constants
• The equilibrium constant measures the extent to which a reversible reaction will occur at a given temperature
• Kc = concentration of products / concentration of reactants
• Can be measures in terms of concentration (Kc) or partial pressures (Kp)
• Kp = p(products) / p(reactants)
• Partial pressure = mole fraction x total pressure
• Mole fraction = moles of chemical species / total number of moles
• Total and entropy change and the equilibrium constant
• total entropy = R lnK
• This means that as a change in temperature causes a change in the total entropy, the value of the equilibrium constant will change too
• Exothermic reaction - increase in temp will cause entropy of surroundings to be less +ve = total entropy smaller = K smaller
• Endothermic reaction -increase in temp will cause entropy of surroundings to be less -ve = total entropy larger = K larger
• Le Chatelier's principle
• If a system at equilibrium is disturbed, the the position of equilibrium will shift to oppose the effects of the change, and restore equilibrium