UNIT 1: SECTION 5 - KINETICS, EQUILIBRIA, and REDOX Flashcards
Equation for reaction rates?
Rate of reaction =
Amount of reac. used/ prod. formed/
Time
What is particle collision theory?
Particles must collide with enough Ea and in the correct orientation to react successfully.
Low Ea - Easier
High Ea - Harder - heating helps.
What effect does a catalyst have on reactions?
- Increases ROR.
- Provides alternative chemical pathway with lower Ea; catalyst not used up.
- Cost-efficient
- Only need little bit.
What effect does increasing temperature have on ROR?
- Rate of reaction increases.
- particles gain more Ek; move faster.
- greater proportion have Ek > Ea.
- on a maxwell boltzmann distrib. curve, graph is more smooth and lower.
What does increasing conc./pressure do to the ROR?
Increasing conc. has the same effect as increasing pressure.
Increases ROR.
More particles in a given space; collision more frequent.
3 ways to measure RoR?
1) Timing the formation of precipitate.
- how long X takes to disappear.
- subjective.
2) Measuring decrease in mass.
- gaseous products evaporate; mass balance mixture before and after.
3) Measuring vol. of gas given off.
- uses gas syringe.
What is dynamic equilibrium?
When the forward reaction rate equals the reverse reaction rate.
The concentration of the reac/prods are constant, and dynamic equilibrium only occurs in closed systems.
State Le Chatalier’s principle.
If a reaction at equilibrium is subjected to any change (pressure, temp, concentration) position will shift to counter these effects.
What effect does temperature have on a reaction at equilibrium?
- An increase would cause equilibrium to shift to the endothermic side.
[TO ABSORB HEAT FROM HOT SURROUNDINGS] - A decrease would cause equilibrium to shift to exothermic side.
[TO GIVE OFF HEAT TO COLDER SURROUNDINGS]
What effect does a change to pressure have on equilibrium?
- An increase in pressure would cause equilibrium to shift to the side with fewer moles. [TO REDUCE PRESSURE]
- A decrease in pressure would cause equilibrium to shift to the side with more moles.
[TO INCREASE PRESSURE]
What effect would a change in concentration have on equilibrium?
- An increase would cause the equilibrium to shift to the side of the products [TO DECREASE CONCENTRATION]
- A decrease would cause the equilibrium to shift to the reactants side [TO INCREASE CONCENTRATION]
What effect would a catalyst have on the equilibrium?
NO EFFECT; can’t increase yield
BUT means equilibrium is reached faster.
Equation for Kc?
aA + bB cC + dD
Kc = [C]^c X [D]^d / [A]^a X [B]^b
How do we work out Equilibrium Conc?
PCl5 —> PCl3 + Cl2
Eg. 0.20 moles of PCl5 decomposes at 600K in 5dm3. Equilibrium mixture contains 0.80 moles of Cl2. Write an expression for Kc and the value and the units.
PCl5 PCl3 + Cl2
I. 0.20 0 0
C. -0.80 +0.80 +0.80
E. 0.12 0.80 0.80
All moles in Equilibrium Mix found so we can work out concentrations by C = n/v
- 80 / 5 = 0.016moldm-3 (Cl2 & PCl3)
- 12 / 5 = 0.024moldm-3 (PCl5)
PCl3 X Cl2 / PCl5 =
0.016^2 / 0.024 =
0.011moldm-3
How does temperature affect Kc?
Increase in temp. -> increase in product (vice versa).
More product, Kc rises because:
Kc = Product / Reactants
More reactants (decrease in temp) -> decrease in Kc.
