Rates and equilibria Flashcards
What is the rate of reaction?
How fast a reactant is used up/product formed.
How does rate change over the course of a reaction?
It is fastest at the start as there is a high concentration which slows as the reaction continues. The limiting reactant is fully used up and rate = 0.
What is collision theory?
It states particles must collide with correct orientation and sufficient energy for a reaction to occur and overcome activation energy.
How can the rate of reaction be increased?
- Increase concentration - increase particles in same vol
- Increase pressure - gas compressed increases concentration- closer
- Increase temperature - particles gain KE and have more energy of activation - can react
How can the progress of a reaction be seen?
Decreasing concentration of reactant/increasing concentration of product. If gas is produced, measure the volume of gas at regular intervals OR loss of mass of reactants with balance.
What is a catalyst?
It increase reaction rate by providing an alternative pathway with lower activation energy. Is chemically unchanged/regenerated.
May form an intermediate or provide reaction surface.
What is a homogenous catalyst?
Same physical state as reactants - forms an intermediate.
What are the 2 types of catalysts?
Homogeneous and heterogeneous
What is a heterogeneous catalyst?
Different physical state as reactants.
Usually solids with gas/aq reactants. Reactant adsorbed onto catalyst surface. eg Haber process.
Why are catalysts important?
Economically, increase sustainability as decrease temperature so less energy demand from fossil fuels - less CO2. High atom economy and fewer pollutants.
What does a Boltzmann distribution show?
The distribution in energy of a sample of particles in fluids. Only a small proportion have more than the activation energy to react.
Area under curve shows total number of molecules. No max energy for a molecule and no particles have 0 zero.
What does a Boltzmann look like if temperature increases?
Greater proportion of collisions - greater area to right of activation energy. Wider spread of values. Increase in rate.
What does a Boltzmann look like if a catalyst is used?
More molecules react, so activation energy moves to the left.
What is dynamic equilibrium?
Forward and backwards reactions occur at the same rate in a closed system. No reactants/products can enter/escape.
What is Le Chatalier’s principle?
When equilibrium is subjected to external change, the system reacts in a way to oppose the effect of the change.
What factors affect the position of equilibrium?
- Concentration - changes rate of 1 reaction
- Temperature - depends if exothermic or endothermic (same number, opposite signs)
- Pressure - proportional to its concentration - side with fewer gas moles
How does a catalyst affect the position of equilibrium ?
No effect - speeds up both rates equally. Increases the rate equilibrium is established.
What are main features of equilibrium?
Equilibrium can be approached from either side
Reactants and products are always present
Concentration of both stays constant
What is the equilibrium constant?
The exact position of equilibrium is calculated in terms of concentration at constant temperature.
What do different Kc values mean?
1: position is halfway
>1: towards products
<1: towards reactants
