It’s all about the …..

Equations at Equilibrium

N2 + O2 + heat 2 NO

Reactions that do not reach completion may stop at an equilibrium point.That is to say that the amount of reactant becoming product is equal to the amount of product changing back into the reactant.

LeChatelier’s Principle

• If we add stress we can force the amount of the reactants and products to change.

• Changes happen to alleviate the stress.

What causes stress?

Ok true but……LeChatelier was referring to different kinds of stress.

What causes stress?

If additional quantities of a chemical are added to the reaction the equilibrium will shift toward the side of the equation that contains fewer molecules.

Given the reaction:

2 KBr + I2(g) 2 KI + Br2(g)

If we added additional I2(g) to the system which direction would the equation shift?

Given the reaction:

2 KBr + I2(g) 2 KI + Br2(g)

If we added additional I2(g) to the system which direction would the equation shift?

Answer:

Addition of I2(g) would allow more reactants to come together to form more products, therefore shifting toward the product side.

Addition of Chemicals Practice:1. For the following reaction: N2(g) + 3H2(g) 2NH3 (g)

Which direction would the reaction shift if more nitrogen gas was added?

2. For the following reaction: NH3(g) + HCl (g) NH4Cl (s)

Which direction would the reaction shift if more NH4Cl (s)

was added?

3. For the following reaction: CO2(g) +MgO(s) MgCO3(s)

Which direction would the reaction shift if more MgO(s) was added?

Addition of Chemicals Practice:1. For the following reaction: N2(g) + 3H2(g) 2NH3 (g)

Which direction would the reaction shift if more nitrogen gas was added?

Shift toward the products.

2. For the following reaction: NH3(g) + HCl (g) NH4Cl (s)

Which direction would the reaction shift if more NH4Cl (s)

was added?

Shift toward the reactants.

3. For the following reaction: CO2(g) +MgO(s) MgCO3(s)

Which direction would the reaction shift if more MgO(s) was added?

Shift toward the products.

Changes in pressure can only effect systems in which gases are involved.

As the pressure is increased the equilibrium will shift towards the side of the reaction with the least volume. If the pressure is decreased the equilibrium will shift towards the side of the reaction with the higher volume.

H2

H2

O2H2O

H2O

3 moles = 67.2L 2 moles = 44.8L

H2

H2

O2H2O

H2O

Was 44.8LWas 67.2L

For the reaction:

N2(g) + 3Cl2(g) NCl3(g)(22.4L + 67.2L) (22.4L)

Which direction would the reaction shift if pressure was decreased?

Answer: The reaction would shift towards reactants. Remember an decrease in pressure will cause the reaction to shift toward the side with the higher volume.

Changes in Pressure Practice:

1. For the reaction: PCl3(g) + Cl2(g) PCl5(g)

What direction would the reaction shift if pressure was increased?

2. For the reaction: CO(g) + 2H2(g) CH3OH(g)

What direction would the reaction shift if pressure was increased?

3. For the reaction: PCl3(g) + 3 NH3(g) P(NH2)3(g) + 3 HCl(g)

What direction would the reaction shift if pressure was decreased?

Changes in Pressure Practice:

1. For the reaction: PCl3(g) + Cl2(g) PCl5(g)What direction would the reaction shift if pressure was increased?Original volumes: Reactants=(22.4L+22.4L) Products=(22.4L)The reaction will shift toward the products.

2. For the reaction: CO(g) + 2H2(g) CH3OH(g)What direction would the reaction shift if pressure decreases?Original volumes: Reactants=(22.4L+44.8L) Products=(22.4L)The reaction will shift toward the reactants.

3. For the reaction: PCl3(g) + 3 NH3(g) P(NH2)3(g) + 3 HCl(g)What direction would the reaction shift if pressure was decreased?Original volumes: R=(22.4L+67.2L) P=(22.4L+67.2L)The reaction will remain the same, the volumes on both sides are equal.

Before you can decide how temperature will effect the equilibrium, you must first identify if the equation is endothermic or exothermic.

If the temperature is raised in an exothermic reaction the reaction will shift towards the reactants. If the temperature is raised in an endothermic reaction the reaction will shift towards the products.

N2(g) + 3H2(g) 2NH3(g) + heat

Increasing the temperature of thisReaction will cause it to shift towardsThe reactants.

N2(g) + 3H2(g) 2NH3(g) + heat

Increasing the temperature of thisReaction will cause it to shift towardsThe reactants.

CaCO3(s) + heat CaO(s) + CO2(g)

Reducing the temperature of this reaction Will cause it to shift towards the reactants.

CaCO3(s) + heat CaO(s) + CO2(g)

Reducing the temperature of this reaction Will cause it to shift towards the reactants.

Change in Temperature Practice:

1. For the reaction: SO3(g) + H2O(l) H2SO4(aq) + heat

In which direction would the reaction shift if temperature was increased?

2. For the reaction: N2(g) + O2(g) + heat 2NO(g)

In which direction would the reaction shift if the temperature was increased?

3. For the reaction: 2 SO2(g) + O2(g) 2 SO3(g) + heat

In which direction would the reaction shift if the temperature was decreased?

Change in Temperature Practice:

1. For the reaction: SO3(g) + H2O(l) H2SO4(aq) + heat

In which direction would the reaction shift if temperature was increased?

The reaction would shift towards the reactants.

2. For the reaction: N2(g) + O2(g) + heat 2NO(g)

In which direction would the reaction shift if the temperature was increased?

The reaction would shift towards the products.

3. For the reaction: 2 SO2(g) + O2(g) 2 SO3(g) + heat

In which direction would the reaction shift if the temperature was decreased?

The reaction would shift towards the products.

HOMEWORK:

Complete the LeChatelier’s worksheet questions 1-12. Return them to Ms. Besal or Mrs. Zado for credit!