Chapter 6 Section 6.3 Nature of Reactions

 Reactions that can change direction  To signify, we use a double set of arrows  The reaction favors the direction that produces the most stable (least likely to change) products Reversible Reactions:

 In a chemical reaction, this is the point at which there is no change in the amount of reactants and products; meaning you will never use up all of your reactants, because the products are always there to form them Equilibrium:

 In a reversible reaction this occurs when opposite actions are taking place at the same rate; products occur at the same rate as the reactants For example, if you are rowing upstream at exactly the same rate as the downstream current, the boat has no net movement Dynamic Equilibrium

LE CHATELIER’S PRINCIPLE: A system will readjust to reduce the disturbance and regain equilibrium If we disturb a reaction at equilibrium, we can obtain more product Changing Direction/Stressing the System : Le Châtelier's Principle

This disturbance can be achieved by:  removing the products as they are created,  adding more reactants  adding or removing energy (endo and exo) Changing Direction/Stressing the System : Le Châtelier's Principle

(1)Removing a product from a reaction at equilibrium will allow more reactants to go on and form more products so that balance is regained (Right) (2) Adding more reactants to a reaction at equilibrium means more products must be made (Right) (3) Adding or removing energy (heat) can move the reaction direction Changing Direction/Stressing the System : Le Châtelier's Principle

the amount of energy that the particles of two substances must have to cause a chemical change to take place; this amount of energy required varies depending on the reaction Activation Energy

Speed of Reaction: How can it be changed? Reaction Rate

1) Temperature : most reactions will go faster at higher temps; lowering the temp will slow most reactions down 2) Concentration : increasing the amount of substance present in a certain volume will generally increase the rate of reaction 3) Surface Area : increasing the surface area of the reactant will increase the rate of reaction Reaction Rate

4) Catalyst : a substance that when added to a reaction can speed up the rate without changing itself; enzymes are examples of biological catalysts Inhibitor : a substance that can SLOW a reaction down; preservatives in food are examples of inhibitors Reaction Rate

the reactant that you run out of first; using it up makes the reaction stop Example: If you have 10 wheels and 4 frames, how many bikes can you build? Only 4…what is your limiting reactant? The frames. Why? They ran out before the wheels! Limiting Reactant

Example: Use the balanced chemical equation to answer the question: 2Na + Cl 2 → 2NaCl  If you have 12 units of sodium and 8 units of chlorine, how many units of sodium chloride can you make? Why? Identify your limiting reactant AND calculate how much excess reactant you have Limiting Reactant