equilibria flashcards
What is the definition of dynamic equilibrium ?
A reversible reaction in which the forward and backward reactions proceeding at equal rate
(And the) concentration / moles of reactants and products remain constant
State the meaning of a closed system ?
A system in which none of the reactants or products can escape
State Chatelier’s principle
If a change is made to a system at dynamic equilibrium
The position of equilibrium moves to counteract / oppose the change that has been made;
What will the magnitude of Kc tell you about the reaction ?
If Kc is very large (Kc»_space;1) the equilibrium lies to the RHS so the reaction mixture contains mostly products
If Kc is very small (Kc «_space;1) the equilibrium lies to the LHS so the reaction mixture contains mostly reactants
If Kc is close to 1 (0.10 < Kc < 1), the mixture contains a similar concentration of both reactant and products
C2H4 (g) + H2O (g) reacts reversibly to produce C2H5OH (g)
Using the Chatelier’s principle, state the effect if any that increasing the overall pressure would have had on the equilibrium yield of ethanol
- The yield of ethanol would increase
- According to Le Chatelier’s principle) increasing the pressure shifts (the position of) equilibrium to the side with the fewest number of (gas) molecules
- to counteract the increase in pressure
Use the Chatelier’s principle to suggest whether a high or low temp should have been used to maximise yield of ethanol. Suggest a problem with using this temperature
-Low (temperature)
-The forward reaction is exothermic / the forward reaction releases heat
- At a lower temperature) the (position of) equilibrium would shift to the right hand side / towards the products / move to increase the temperature / release heat energy
A low temperature can result in a) slow rate of reaction
CO2 (g) + 3 H2 (g) reacts reversibly to produce CH3OH (g) + H2O (g)
state and explain the effect that using a catalyst will have on the yield of methanol
- No effect on / no change to the yield of methanol produced
- (Because) a catalyst speeds up the rate of the forward and backward reaction equally
- Position of equilibrium is unchanged
State and explain why a lower temperature will increase the yield of methanol but a lower pressure will decrease the yield of methanol.
- The forward reaction is exothermic
- (The position of equilibrium has shifted) to counteract the changes made / to increase the temperature
- So the (position of) equilibrium will to shift/move to the right hand side / towards the products, so yield of methanol inc
- There are less/fewer/a smaller number of molecules of gas on the right hand side
- so the equilibrium shifts to increase the pressure and moves to the LHS, so yield of methanol dec
Give a reason why scientists in industry much prefer to use low temperatures and pressures
( 1 mark)
(High pressure and temperature) can be (very) expensive
OR
(High pressure and temperature) can be dangerous;
N2 + O2 react reversibly to produce 2 NO
when the temp of the system increases, the yield of NO increases.
State and explain whether the forward reaction is endo or exothermic
- The forward reaction is) endothermic
- (When temperature was increased) the position of equilibrium shifted/moved to the right hand side;
- To oppose the change and decrease temperature
State and explain the effect on the yield of NO if the temp stays the same but the pressure is increased
- (There would be) no effect
- There are the same/equal number of molecules of gases on both sides of the equation
- There will be no change to the position of equilibrium;
State how the students could make sure that a reaction mixture has reached equilibrium
- Taking several samples and testing them starting after 24 hours have passed
- to make sure tey get the same test results each time
