Equilibria Flashcards
What does dynamic equilibrium mean?
Rate of forward reaction = rate of backward reaction
Explain Le Chatelier’s principle
If a system at equilibrium is disturbed, the equilibrium moves in the direction that reduces the disturbance
Changing what factors can alter the position of equilibrium?
- Concentration of reactants or products
- Pressure
- Temperature
What effect would increasing the temp have on the position of the equilibrium?
CH4 + H2O = CO + 3H2 +210 kJmol-1
The equilibrium positions shifts to the right
What effect would increasing pressure have on the position of equilibrium?
CH4 + H2O = CO + 3H2 +210 kJmol-1
Shifts to the left
Suggest and explain why an industrial chemist may use high pressure for the production of hydrogen?
CH4 + H2O = CO + 3H2 +210 kJmol-1
- High pressure increases the collision frequency thus increases rate of reaction
- This is a compromise pressure between an economically viable rate of reaction and a slightly lower yield of hydrogen
What effect does a catalyst have on the position of the equilibrium?
No effect because it affects rate of forward and backward reaction equally
What condition affects the value of Kc?
Temperature
What does Kc being greater or less than 1 suggest for the position of equilibrium?
Kc > 1 shifts to right
Kc < 1 shifts to left
What effect does decreasing the temperature in an endothermic reaction have on Kc?
Kc decreases
What effect does increasing temperature on an endothermic reaction have on Kc?
Kc increases
What effect does decreasing the temperature of an exothermic reaction have on Kc?
Kc increases
What 2 conditions needs to be met for a collision to be effective?
- The particles need to collide with the correct orientation
- The particles have sufficient energy to overcome Ea barrier
How does increasing conc affect the rate of reaction?
- An increase in conc increases the number of particles in the same volume
- The particles are closer together so collide more frequently
How does increasing pressure of a gas affect the rate of reaction?
- The conc of gas molecules increase as the same number of gas molecules occupy a smaller volume
- The gas molecules are closer together and collide more frequently leading to more effective collisions
What are 2 methods that can be used to determine the rate of reaction of a gas?
- Monitoring the volume of gas produced at regular intervals through gas collection
- Monitoring the loss of mass of reactants using a balance
What is the method for monitoring the production of gas using gas collection of hydrogen peroxide?
- Add hydrogen peroxide to a conical flask
- Measure the initial gas in the measuring cylinder
- Add manganese dioxide, catalyst, to the conical flask and put the bung on
- Measure the gas produced at regular intervals until no more gas is produced
What is the method to monitoring the loss of mass of reactants using a balance?
- Add calcium carbonate and HCl to a flask on a balance
- The mass of the flask is recorded initially and at regular intervals
What is a homogeneous catalyst?
Has the same physical state as the reactants?
What is a heterogeneous catalsyt?
Has a different physical state from the reactants
Using boltzmann distribution, what effect does an increase in temp have on molecules?
- The graph is stretched over a greater range of energy values
- More molecules have an energy greater than or equal to the Ea, so a greater proportion of collisions
- The peak is lower and shifted to the right
Using boltzmann distribution, what effect does a catalst have on molecules?
- A catalst provides an alternative route with a lower Ea
- The Ea is reduced so now a greater proportion of molecules can overcome the Ea
What is the equation for the haber process?
N2 + 3H2 -> 2NH3
State the temperature and pressure that are used in the Haber process
100 atm
500 degrees
Why are the conditions in the Haber process a compromise between rate and equilibrium?
- Increased pressure because there are molecules on the LHS
- Increased temp increases rate because more molecules have more energy
- Increased pressure increases rate as molecules are more concentrated
- Increased temp pushes equilibrium to the left as forward reaction is exothermic
- If temp too high, low yield
- If temp too low, slow rate
Use collision theory to explain the changes in the rate of reaction as it proceeds
- Concentration decreases gradually
- Rate of collision decreases
- Reaction stops when all of one reagent is used up
Suggest 2 ways in which the use of catalysts help chemical companies to make their processes more sustainable
- Not used up so better atom economy
- Less CO2 emitted so less harmful toxins in the environment
What is homogeneous equilibria?
- Kc expression written as normal
- All species are in the same state
What is heterogeneous equilibria?
- Species are in different states
- Don’t include solids and liquids
What type of bracket is used for partial pressure?
(X)
How do you calculate partial pressure continuing from an ICE table?
- Add all equilibrium moles
- Divide mole/total moles
- Multiple by sum of partial pressures
What is the equation for (CH3COOH)2 (g) ⇌ 2CH3COOH (g)
kP = p((CH3COOH2))/p(CH3COOH)2
