Equilibrium

• The symbol for a reversible reaction is ⇋
• An exothermic reaction releases energy
• What temperature change would you see in an endothermic reaction?

  From 35 to 25 degrees
• What are the products when ammonium chloride is thermally decomposed?

  Ammonia and hydrogen chloride
• What is not a reversible reaction?

  Reacting magnesium metal and nitric acid
• Hydrated crystals of copper sulphate have what colour?

  Blue
• When heated, hydrated copper sulphate crystals (blue) turn to a white powder. When water is added the powder turns blue again. The last change described is exothermic.
• Closed system - a reaction where matter and energy can not be gained or lost from the environment
• Open system - a reaction where matter and energy can be gained or lost from the environment
• Exothermic - a reaction where energy is given out
• Endothermic - a reaction where energy is taken in
• Equilibrium - when the forward and backward reactions happen at the same rate
• Reversible reaction - a chemical reaction that can go both ways
• The hydration of copper sulfate is a reversible chemical reaction that can be used as a test for water
• In a reversible reaction, if the forward reaction is exothermic the reverse reaction will be endothermic
• A ⇋ in an equation shows a reversible reaction
• In a reversible reaction, reactants make products and products make reactants under the same conditions.
• Reversible reactions that are exothermic in one direction are endothermic in the opposite direction. Both transfer the same amount of energy. If no reactants or products escape, equilibrium is reached when the forward and reverse reactions occur at exactly the same rate.
• If a change is made to any of the conditions, then the system changes. This can be predicted by Le Chatelier's Principle.
• The chemicals that go into a reaction are called the reactants. The chemicals that are made in a reaction are called the products. Most reactions are irreversible, but some reactions are reversible. This means that the products can react to produce the original reactants again. To show this in a chemical equation, we use two arrows, each with just half an arrowhead:  ⇌
• The A + B turning into C + D is the forwards reaction and the C+D turning back into A + B is the backwards reaction (also called the reversed reaction).
• If the chemical reactions happen in a container where one or more of the reactants or products can escape, you have an open system. If the reaction happens in a container where none of the reactants or products can escape, you have a closed system- these reactions will eventually reach equilibrium. This is when the forward reaction and the reversed reaction happen at the same rate. Changing the reaction conditions  can change the amounts of products and reactants in a reaction mixture at equilibrium.
• When there is a change in conditions in a closed system at equilibrium, the position of equilibrium shifts so that it cancels out the change. These can be conditions such as concentration, temperature or pressure.This principle is called Le Chatelier’s Principle.