Equillibrium - Topic 10 Flashcards
When does dynamic equilibrium occur
Dynamic equilibrium occurs when forward and backward reactions are occurring at equal rates. The concentrations of reactants and products stays constant and the reaction is continuous
What is the effect on temperature on the equilibrium
- If temperature is increased the equilibrium will shift to oppose this and move in the endothermic direction to try to reduce the temperature by absorbing heat.
- If temperature is decreased the equilibrium will shift to oppose this and move in the exothermic direction to try to increase the temperature by giving out heat.
What effect would increasing temperature have on the yield of ammonia?
N2 + 3H2 ——> 2NH3 enthalpy = -280 kjmol-1
If temperature is increased the equilibrium will shift to oppose this and move in the endothermic, backwards direction to try to decrease temperature. The position of equilibrium will shift towards the left, giving a lower yield of ammonia.
What does Le Chatelier’s principle state
Le Chatelier’s principle states that if an external condition is changed the equilibrium will shift to oppose the change
What is the effect in pressure in equilibrium
- Increasing pressure will cause the equilibrium to shift towards the side with fewer moles of gas to oppose the change and thereby reduce the pressure
- Decreasing pressure will cause the equilibrium to shift towards the side with more moles of gas to oppose the change and thereby increase the pressure
- If the number of moles of gas is the same on both sides of the equation then changing pressure will have no effect on the position of equilibrium
MOLES OF GAS = BIG NUMBER infront of the compounds in a reaction
What effect would increasing pressure have on the yield of methanol?
CO (g) + 2H2(g) —-> CH3OH (g)
If pressure is increased the equilibrium will shift to oppose this and move towards the side with fewer moles of gas to try to reduce the pressure. The position of equilibrium will shift towards the right because there are 3 moles of gas on the left but only 1 mole of gas on the right, giving a higher yield of methanol
Different industrial processes which uses equilibrium
- Haber process
- Contact process
- Production of methanol from CO
- Hydration of ethene to produce ethanol
Effect on concentration on equilibrium
- Increasing the concentration will cause the equilibrium to shift in the direction of the lower concentration to oppose the change
- Decreasing the concentration will cause the equilibrium to shift in the direction of the higher concentration
Effect of a catalyst on equilibrium
A catalyst will have no effect on the position of equilibrium but it will speed up the rate at which equilibrium is achieved this is because it speeds up the rate of the forward and backward reaction by the same amount
Conditions of the Haber process
Temp: 450
Pressure: 200-1000 atm
Catalyst: iron
How does equilibrium apply to the Haber process
- As the forward reaction is exothermic we would need a low temperature to produce a good yield of ammonia but this would mean that the ammonia would be produced at a slow rate this means that a compromise temp of 450 is used
- high pressure gives a good yield and a high rate but too much pressure would lead to high energy cost for pumps to produce the pressure
Haber process reaction
N2 + 3H2 ⇌ 2NH3 (exothermic reaction)
Conditions of Contact process
Temp: 450
Pressure: 1 to 2 atm
Catalyst: V2O5
What only affects kc
Temperature nothing else
Equation for contact process
Stage 1 S (s) + 02(g) → S02 (g)
Stage 2 SO2 (g) + ½/02 (g) - reversible reaction - SO3 (g)
Effect on temp and pressure on contact process
Low temp gives good yield but slow rate so 450 degrees is used
High pressure gives slightly better yield and high rate but too high a pressure would lead to too high energy costs for pumps to produce the pressure
What are the effects of pressure and temperature on haber and contact processes
Low temp gives good yield but slow rate: compromise moderate temp used
High pressure gives slightly better yield and high rate: too high a pressure would lead to too high energy costs for pumps to produce the pressure
What are the effects of pressure and temperature on haber and contact processes
Low temp gives good yield but slow rate: compromise moderate temp used
High pressure gives slightly better yield and high rate: too high a pressure would lead to too high energy costs for pumps to produce the pressure
What are the effects of temperature and pressure for production of methanol form CO and hydration of ethene
Low temp gives good yield but slow rate: compromise temp used
High pressure gives good yield and high rate: too high a pressure would lead to too high energy costs for pumps to produce the pressure
For hydration only - High pressure also leads to unwanted polymerisation of ethene to poly(ethene)
Production of methanol from CO equation
CO (g) + 2H2(g)- reversible reaction - СН3ОН (g)
Conditions of production of methanol from CO
T= 400°C, P= 50 atm, catalyst = chromium and zinc oxides
Conditions of production of methanol from CO
T= 400°C, P= 50 atm, catalyst = chromium and zinc oxides
Equation for production of methanol from CO
CO (g) + 2H2 (g) - reversible reaction - СН3ОН (g)
Equation for hydration of ethene to produce ethanol
C2H4 + H20 -reversible reactions - C2H5OH
Conditions for hydration of ethene to form ethanol
T= 300°C, P= 70 atm, catalyst = conc H3P04
What can having a large and small kc tell us
The larger the kc the equilibrium favours the products
The smaller the kc the equilibrium favours the reactants
What can having a large and small kc tell us
The larger the kc the equilibrium favours the products
The smaller the kc the equilibrium favours the reactants
What is the effect of increasing the concentration of OH ions and H ions in this reaction I2 + 2OH- (BROWN). <—> I- + IO- + H2O (COLOURLESS)
Increasing the concentration OH ions causes the equilibrium to shift to oppose this and move in the forward direction to remove OH ions. The position of equilibrium will shift towards the right, giving a higher yield of I’ and
IO-. ( The colour would change from brown to colourless)
Adding H+ ions reacts with the OH ions and reduces their concentration so the equilibrium shifts back to the left giving brown colour.
