Chemistry - Unit 1: Equilibrium

What 3 main things occur when a chemical reaction reaches equilibrium?

What 3 main things occur when a chemical reaction reaches equilibrium?

1. Forward and reverse reactions are taking place at the same rate.

2. Reactions do not reach completion.

3. Concentrations of reactants and products are no longer changing.

What remains constant at equilibrium?

Macroscopic changes; pressure, temperature, colour change / pH, concentration remain constant. (No Macroscopic changes)

How can you tell the solubility of species within a equilibrium equation?

If reactants are favoured, then there is low solubility.

If products are favoured, there is high solubility.

Can there be equilibrium if there are more reactants and products or more products than reactants?

Yes, there can be more reactants or more products present at equilibrium. However, there is no further changes at equilibrium.

What are macroscopic changes?

Observable changes (pressure, temperature, colour change / pH, concentration)

What is dynamic equilibrium?

The forward and reverse process occurs, even though the reaction has stopped.

What can help identify the position of equilibrium? How can you tell if reactants or products are favoured?

1. Percent reaction / yeild Reactants favoured: <50% Products favoured: >50%

2. Equilibrium Constant Reactants favoured: Kc < 1 Products favoured: Kc > 1 Nothing favoured: Kc = 1

What does it mean when a reaction is quantitative? What shows that a reaction is quantitative?

1. The reaction goes to completion and that more than 99% of limiting reagent is used up.

2. Forward arrow represents quantitative.

What is a concentration profile?

It is a type of graph that is Concentration vs. time and it shows if products or reactants are increasing or decreasing to reach equilibrium. It also shows when Equilibrium has been reached.

What characteristics have an effect on the Equilibrium constant? What does not?

Temperature does have an effect on the equilibrium constant. Pressure and concentration do not.

Does the Kc value remain constant during equilibrium?

Yes, there is a constant ratio between reactants and products at equilibrium. If the temperature remains constant, then Kc / Equilibrium constant will remain constant.

What are the laws of Kc (equilibrium constant)?

1. Equilibrium law expression only can include substances with varying concentrations.

• gases are included because their concentrations vary depending on pressure.

• aqueous solutions are included because their concentrations vary depending on volume.

• mixtures of liquids are included because they vary from dilution of one another (2 or more liquids).

• solids are not included.

• pure liquids are not included (lone liquid).

What is the only macroscopic change that will affect the Kc value?

Temperature.

What determines if a reaction that has reached an equilibrium state is homogeneous or heterogeneous?

Homogeneous: Reactants and products are all in the same phase. Heterogeneous: Reactants and products are not all in the same phase.

What is La Chatelier's Principle?

When a chemical system at equilibrium is disturbed by a change in a property, the system adjusts in a way that opposes this change.

What is La Chat's principle with concentration changes?

1. Addition of reactant / removal of product: Increase in overall yield of product - SHIFT RIGHT.

2. Increase in concentration of chemical: SHIFT AWAY from increased chemical.

3. Decrease in concentration of chemical: SHIFT TOWARD to decreased chemical.

• Use arrow method

What is the definition of a Exothermic / Endothermic reaction?

Exothermic: Bonds are formed, and Energy is released as products. Endothermic: Bonds are broken, and energy is a reactant.

In an exothermic equilibrium reaction, what happens when temperature or KC value is increased or decreased?

Temperature increase = KC value decrease

Temperature decrease = KC value increase

** inverse relationship

In an endothermic equilibrium reaction, what happens when temperature and KC value are increased or decreased?

Temperature increase = KC value increase

Temperature decrease = KC value decrease

** proportional relationship

What sign is Exothermic / Endothermic energy denoted as?

Exothermic: Negative energy (E= +ve) Endothermic: Positive energy (E= -ve)

What is La Chat's principle with temperature changes?

1. System is cooled: Shifts so more heat is produced.

2. System is heated: Shifts toward energy is being used.

*Equilibrium will shift to minimize change / use arrow method

What is La Chat's Principle with pressure / volume changes?

1. Increase in volume / Decrease in pressure: SHIFT TOWARD LARGER MOLS (more gaseous entities)

2. Decrease in volume / increase in pressure: SHIFT TOWARD LESSER MOLS (less gaseous entities)

3. Equal number of mols / gaseous entities: NO SHIFT (not affect by change in volume)

Are Equilibrium concentrations affected by outside forces, if so what are they?

They can be affected by a change in temperature, pressure / volume, and concentration.

Are systems with liquids or solids affected by changes in pressure / volume?

If a system ONLY involves liquids or solids, it is NOT affected by changes in pressure / volume.

What do Catalysts do to equilibrium vs. what inert gases do to equilibrium?

Both do NOT affect the equilibrium concentration / position of equilibrium.

What speeds up reaction and what slows down a reaction?

1.Catalyst speeds up the rate of the reaction in the forward and reverse direction equally. 2. Inert gases slow down the rate of the reaction in the forward and reverse direction equally.

If there is only one spike present for a reaction at a specific time on a La Chat graph, what happened?

If there is only one spike for a certain time then one of the products or reactants have increased or decreased in concentration. The other compounds/elements will go up or down depending on the shift.

If there are no spikes present for a reaction at a certain time on a La Chat graph, what happened?

There was a temperature stress.

If there are only spikes present at specific time on a La Chat graph, what happened?

There was a change in volume / pressure.

Why does the entire system of a reaction spike in a certain direction when there is a volume/ pressure change?

Decrease in volume / Increase in pressure = Immediate concentration increase for the entire system. (Spike up) Increase in volume / Decrease in pressure = Immediate concentration decrease for the entire system. (Spike down)

Are liquids / solids affected by Pressure / volume changes?

No, only gaseous / aqueous substances are.