10.4

Question 1

What is dynamic equilibrium?

Answer 1

What is a closed system?

• Isolated from the surroundings so no substance can enter or leave

What is dynamic equilibrium?

• the rate of forward reaction is equal to the backward reaction/ reversible reaction is where the products can react to reform the original reactants
• Concentration of reactants and products is the same
• Takes place in a closed system only-unaffected from outside influences

Question 2

What is Le Chatliers principle?

Answer 2

If a change (pressure, temperature or concentration) is imposed in a system of dynamic equilibrium, the position of equilibrium would shift in the direction that partly compensates/counteracts for that change

Question 3

What happens if you increase the temp, what happens to the position of equilibrium?

Answer 3

• Increase in temperature shifts the position of equilibrium in endothermic direction
• Decrease in temperature, the position of equilibrium shifts to the exothermic reaction

Question 4

What happens to the position of equilibrium if you increase the pressure?

Answer 4

Increase in pressure shifts the position of equilibrium in side with less moles of gas
Only works in homogenous equilibria (reactants and products in the same state)

Question 5

What happens if you increase the concentration?

Answer 5

increasing the concentration of reactants the rate of forward reaction increases therefore the position of equilibrium shifts to the right so we get more products
If we increase the concentration of products we get more reactants

Question 6

How do catalysts affect the position of equilibrium?

Answer 6

• Catalyst speeds up the rate of reaction at the same rate/equally (forward and backward reaction) but the position of equilibrium remains the same.
• It allows a reaction to reach equilibrium faster but no affect on yield

Question 7

What is the Haber process?

Answer 7

• industrial production of ammonia
• Reversible exothermic reaction
• 200 ATM pressure and 450 degrees

Question 8

How can ethanol can be formed then ethene and steam?

Answer 8

• Ethanol is produced via the reversible reaction with ethene and steam
  C2H4 + H20 (g) —-> C2H50H (g)
• The reaction can be carried out at a pressure of 60-70 atmospheres and a temp 300 degrees (compromise between yield and rate) with a phosphoric acid (V) catalyst
• in these reactions there is a compromise between maximum yield and expense

Question 9

How does the Kc value affects the position of equilibrium using the value of Kc?

Answer 9

• larger the value of Kc the more products there are at equilibrium, so the further the equilibrium lies to the right
• smaller the value of Kc, the more reactants there are at equilibrium, so further the equilibrium lies to the left.
• if temp changes equilibrium shift to the right Kc will increase but if it shifts to the left Kc will decrease.

The brown gas NO2 exist in equilibrium with the colourless gas N2O4

• place two sealed tubes containing the equilibrium mixture in water baths- one in a warm water bath and one in a cool water bath and observe the colours of the mixture
• the tube in the warm water bath will change to a darker brown colour as the endothermic reaction speeds up to absorb extra heat, pushing equilibrium to the left (endothermic)
• the tube in a cool water bath will lose colour as the exothermic reaction speeds up to try and replace the lost heat, pushing equilibrium to the right.

- to investigate the changing concentration: 
Mixing iron (III) nitrate (yellow) and potassium thiocyanate (colourless) results in a reversible reaction the product is iron (III) thiocyanate. The equilibrium mixture is a reddish colour.

Test tube one is a control so has a slight red colour
Test tube two, adding more Fe3+ so equilibrium shifts to the right more Fe(SCN)3 is produced
Test tube 3, adding more SCN- ions so equilibrium shifts to the right so there is more Fe(SCN)3 produced
Test tube four, add more Fe(SCN)3 so equilibrium shifts to the left so more reactants it will be a yellow

Question 10

What are reversible reactions?

Answer 10

When the reaction can go forward and backward
In the forward reaction, reactants are used up quickly but then slow as their concentration drops
In the backward reaction reactants are reforested slowly but speed up as the concentration of products increase