Chemical Equilibrium
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Are equilibrium processes reversible?
Yes
What does reversible mean in a chemical reaction?
The reaction can take place in either a forward or reverse direction
What is a dynamic equilibrium?
• When reactions are in eqm there seems to be no observable change 2. However, the system is actually in constant motion - it is a dynamic eqm 3. Although you cannot see anything happening, reactants are constantly being converted into products, and likewise, products are converted back into reactants
What are the three features of a dynamic equilibrium?
• In a closed system/environment 2. Rate of forward reaction=rate of reverse reaction 3. Conc (of reactants and products) do not change/ are constantly being constant
What is Le Chatelier’s Principle?
The (position of a dynamic) equilibrium shifts to minimise (the effect of) any change
Explain the three factors that affect the position of equilibrium
• Concentration- Add a chemical (increases conc) - eqm moves to get rid of it, remove a chemical (decrease the conc) - eqm shifts to make more of it 2. Pressure - Raise the pressure - eqm shifts to lower it, lower the pressure - eqm shifts to raise it 3. Temp - increase temp - eqm moves to cool it, decrease temp - eqm moves to heat it
Explain how concentration can affect the position of a dynamic equilibrium
• Increase conc of reactants/decrease conc of products - position of eqm will shift to the right to decrease the conc of reactants/increase the conc of products 2. Decrease conc of reactants/increase conc of products - position of eqm will shift to the left to increase the conc of reactants/decrease the conc of products
Describe how pressure affects the position of a dynamic equilibrium
• Increase pressure - position of eqm will shift to the side with fewer moles i.e. the left/right 2. Decrease pressure - position of eqm will shift to the side with more moles i.e. the left/right
Explain how temperature affects the position of a dynamic equilibrium
• Increase temp - the reaction is endo/exo, the position of eqm will shift in the endo direction i.e. the left/right 2. Decrease temp - the reaction is endo/exo, position of eqm will shift in the exo direction i.e. the left/right
Explain how adding a catalyst affects the position of a dynamic equilibrium
Has no effect on yield or position of eqm. The catalyst increases the rate of both forward and backward reactions equally. Time taken to reach eqm decreases - lower Ea - more particles with E greater than Ea - more frequent successful collisions
What is required to make the highest possible yield of product as quickly and cheaply as possible in industrial equilibrium systems?
Requires a compromise between reaction rate and chemical equilibrium
What are the issues with low temperature in chemical industry?
Decreases rate of reaction
What are the issues with high temperatures in chemical industry?
Increases energy costs
What are the issues with low pressure in chemical industry?
Decreases rate of reaction
What are the issues with high pressure in chemical industry?
Expensive to generate and is a safety risk
What does an equilibrium have to be to able to write an expression for equilibrium constant, Kc?
Homogenous
What does homogenous equilibrium mean?
A system in which the reactants and products are in the same phase
What is Kc?
A ratio of the concentration of products to the reactants
How would you lay out an expression for Kc?
Use template: Kc=[products]/[reactants]
What does [ ] mean in a Kc expression?
The concentration of the species in moldm^-3
How would you calculate a value for Kc?
• Write out a Kc expression 2. The concentrations of the species will be squared by the no. moles 3. Plug in the actual concentrations and calculate a value
Are you required to be able to rearrange Kc equations to find the value for the concentration of a specific substance?
Yes
When can you use moles instead of concentration to calculate a value for Kc?
If Kc has no units (concentrations cancel out) i.e. the same number of moles on both sides
Where does the position of equilibrium lie if Kc is greater than 1?
Lies to the right because it means there is more products than reactants