Changing Temperature

Worked Example:

- Annotate which reaction is exothermic and which is endothermic using ∆H.

Q: How would increasing temperature affect the yield of NH₄Cl?
- Equilibrium shifts to the left to favour the backward endothermic reaction.
- This increases the yield of NH₄Cl.

Q: How would decreasing temperature affect the yield of NH₄Cl?
- Equilibrium shifts to the right, favouring the forward exothermic reaction.
- This decreases the yield of NH₄Cl.

Changing Pressure:

- Pressure = How many particles there are in a given volume?

- More moles of gas = more pressure
- Closed system = no products/reactants are added/removed.
- Changing the pressure of a single substance would affect the entire system.

Worked Example:

- Annotate the number of moles per side for gas (look at the big number).

Q: How would increasing pressure affect the yield of NO₂?
- Equilibrium will shift to the right, favouring the forward reaction.
- There are fewer moles of gas on the right side.
- This decreases the yield of NO₂.

Heating Ammonium Chloride:

- NH₄Cl can be formed by reacting NNH₃ + HCl gas.
- Carefully heat the test tube containing a small amount of NH₄Cl.
- Make sure there’s some mineral wool at the top of the test tube.
- Heating the test tube means NH₄Cl decomposes into hydrogen chloride gas and ammonia gas.

- At the top of the test tube, the 2 gases recombine as it’s cooler to form a white solid → NH₄Cl.

Dynamic Equilibrium:

Features of Dynamic Equilibrium:

- Rates of forward and backward reaction are equal.
- Concentration of reactant(s) + product(s) are constant.

Le Chatelier’s Principle:

- If dynamic equilibrium is disturbed by changing the conditions, the equilibrium's position moves to counteract that change.
- Equilibrium can be affected by changing concentration, pressure, and temperature and adding a catalyst.
- When answering Q’s, mention:
→ shift (right/left)
→ favoured side with (yield)
→ yield (how amounts change)

Changing Concentration:

Worked Example:

Q: How would increasing the concentration of ICl affect the yield of Cl₂?

- Equilibrium shifts to the right, favouring the forward reaction.
- This decreases the yield of Cl₂.

Making ammonia (ideal conditions)

Temperature:

- Equilibrium: Low temperature needed, so reaction shifts right.
- Rate of reaction: High temperature = faster reaction
- Therefore, we must reach a compromise.

Pressure:

- Equilibrium: high pressure, so RHS favoured it.
- Rate of reaction: High pressure = more frequent collisions
- Therefore, high pressure is used (but can be very expensive).

Concentration:

- Equilibrium: High concentration (of reactants) favours RHS + low concentration of products too → remove the product after making.

Catalyst:

- Rate of reaction: This increases the rate of both reactions (but not the yield).