Chapter 6Section 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 reactantsFor 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 reactantsadding 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 down2) Concentration : increasing the amount of substance present in a certain volume will generally increase the rate of reaction3) 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 + Cl2 → 2NaClIf 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