Chemistry 2.6 + 2.4

What are acids?

Proton donors (+, usually)

What are bases?

Proton receptors (-, usually)

What are conjugate pairs?

Acid/base combo that differs between 1 proton. Can switch between acid/base.

Strong acid/base

Fully dissociates in water. Acid produces lots of H₃O⁺ ions, base produces lots of OH^- ions. 

Weak acid/base

Partially dissociates in water. Creates a reversible, two-way reaction which forms an equilibrium.

Acid

pH less than 7

Base

pH greater than 7

Neutral

pH equal to 7

Current

Flow of charge. Flow of charge is due to charged ions, which creates a current.

Conductivity

Conductivity depends on the number of mobile charged particles (can be ions). Strong acids/bases will be more conductive, as they fully dissociate in water producing ions. The amount of charged ions in a solution determines the electrical conductivity of a given solution.

Amphiprotic

A substance that can accept and donate protons e.g. water.

What do acids and bases produce in a solution?

Acids produce hydronium ions (H₃O⁺), bases produce hydroxide ions (OH^-) in a solution. 

When is a two way reaction at equilibrium?

When the forward and reverse reaction is happening at the same rate. Overall effect = we cannot see anything happen as they cancel out.

What does equilibrium not mean?

Equilibrium does not mean the amount of reactants is equal to the amount of products. It also does not mean that the reaction has stopped.

Le Chatelier’s principle

"Any change made to a system in equilibrium results in a shift of the equilibrium in the direction that minimises the charge.”

Catalysts

Catalysts lower the energy required for the reaction to take place (activation energy) + has no effect on equilibrium position. 

Pressure

Increase in pressure favours products, decrease in pressure favours reactants (weak acid/base)

Concentration

If more products are added, the system will ‘add’ more reactants by favouring reactant → product equation. If more reactants are added, the reverse will happen.

Temperature

Exothermic = energy given out to surroundings (change in enthalpy = -). Endothermic = energy taken in from surroundings (change in enthalpy = +).

Temperature and equilibrium

In an equilibrium system, one reaction will be exothermic and the other will be endothermic. In the endothermic reaction, products are favored over the reactants. In an exothermic reaction, the reactants are favoured over the products.

Temperature and K_c

Endothermic causes K_c to increase, exothermic causes K_c to decrease.

K_c

The mathematical representation of the position of the equilibrium, which requires no units. It compares the concentration of products and reactants. K_c = [products] divided by [reactants]

What does K_c not include?

Solids and liquids, as they are constant.

What does K_c include?

Gases and aqueous substances

Collision theory

Reactions involve a transformation, where the reactant particles (atoms or molecules) combine to form products. Particles in a reaction are randomly moving and can be altered with multiple factors. 

Activation energy

The minimum amount of energy required for a chemical reaction to occur between reactant particles.

Concentration

Increase in concentration will increase the frequency of collisions, increasing the reaction rate.

Surface area

An increased surface area will increase the reaction rate, as the surface layers are the only sides a particle can react with to produce products. increased frequency of collisions = increased successful collisions =  increased rate of reaction.

Kinetic energy (form of temperature)

increase in temp → particles gain kinetic energy → frequency of collisions increase → increased successful collisions → increased rate of reaction

Activation energy (form of temperature)

Temp provides the particles the minimum amount of heat energy required. Increase in temp → reaction happens sooner → rate of collisions increase → rate of reactions increase. Decrease in temp → reaction happens less → less collisions → rate of reaction slows.

Endothermic graph

Exothermic graph

Enthalpy calculations

Energy (kJ) = change in enthalpy (kJ mol^-1) x n (number of moles)