Kinetics, equilibria and redox Flashcards
(35 cards)
What is the collision theory?
For a reaction to occur between two particles, they must collide with sufficient energy to break bonds. Most collisions do not lead to a reaction.
What is activation energy?
(Ea) – the minimum energy required for a reaction to occur.
What is the rate of reaction?
The change in concentration of reactant or product, per unit time.
Units = moldm-3s-1.
What are the 5 factors that affect the rate of reaction?
- Temperature
- Concentration of solution
- Pressure of gas
- Surface area of a solid
- Catalyst
How does temperature affect the rate of reaction?
This increases the speed of molecules and their kinetic energy and therefore the frequency of successful collisions also increases.
How does the concentration of a solution affect the rate of reaction?
If there are more particles in a given volume, collisions are more frequent and therefore reaction rate is faster.
How does the pressure of a gas affect the rate of reaction?
If there are more particles in a given volume, collisions are more frequent and therefore reaction rate is faster.
How does the surface area of a solid affect the rate of reaction?
The greater the total surface area of a solid, the more of its particles are available to collide, leading to more frequent collisions due to more sites for reaction.
What is a catalyst?
A chemical which speeds up the rate of a chemical reaction without being used up itself.
How does a catalyst work?
A catalyst works by finding an alternative pathway for a chemical reaction with a lower activation energy.
What does the Maxwell-Boltzmann distribution show?
The Maxwell-Boltzmann Distribution tells us the distribution of energy amongst the particles.
Why does the curve of a Maxwell-Boltzmann distribution start at the origin?
No particles have 0 energy.
What effect does a higher temperature have on a Maxwell-Boltzmann distribution curve?
The peak of the curve is lower and moves to the right. The number of particles with very high energy increases. The total area under the curve is the same for each temperature because it represents the same number of total particles. The curves show that at a higher temperature the reaction rate is faster because more particles have the activation energy.
What is dynamic equilibria?
Dynamic equilibria is when the forwards and backwards reactions are occurring at the same rate, resulting in the concentrations of products and reactants remaining constant.
What is Le Chatelier’s Principle?
- Le Chatelier’s Principle is when a system is in equilibrium, it will oppose any change put upon it.
What 4 factors affect the position of equilibrium?
- Concentration
- Pressure
- Temperature
- Catalysts
How does concentration affect the position of equilibrium?
If the concentration of a reactant is increased, the equilibrium will shift in the direction that tends to reduce the concentration of this reactant
A(aq) + B(aq) ←→ C(aq) + D(aq)
If the concentration of A is increased, the equilibrium will move to the right to reduce the concentration of A, and the yield of C and D will increase.
How does pressure affect the position of equilibrium?
If the pressure is increased, the equilibrium will shift in the direction that tends to reduce the pressure ( the side with the least moles of gas)
3H2 (g) + N2 (g) ←→ 2NH3 (g)
If the pressure is increased, the equilibrium will move to the right to reduce the pressure, and the yield of ammonia will increase. This is because there are 4 moles of gas on the left and only 2 moles of gas on the right.
How does temperature affect the position of equilibrium?
If the temperature is increased, the equilibrium will shift in the direction that tends to lower the temperature (the endothermic side).
2SO2(g) + O2(g) ←→ 2SO3(g) ∆H = -197kJmol-1
The forward reaction is exothermic. If the temperature is increased, the equilibrium will shift in the direction that tends to reduce the temperature (the endothermic side) and so the yield of sulphur trioxide will decrease.
How does a catalyst affect the position of equilibrium?
Catalysts do not affect equilibrium position and yield of product because they speed up the forwards and backwards reactions equally.
What is a compromise condition?
A balance between the rate, yield and cost of a chemical reaction.
- high pressures are too expensive
- low temperatures cause a slow rate of reaction
What is a homogeneous equilibrium?
Homogeneous equilibrium is when every species in a reaction is in the same state.
What is a heterogeneous equilibrium?
Heterogeneous equilibrium is when the species in a reaction are in different states.
What is the only factor that affects kc values?
Temperature
