CHAPTER 10: Reaction Rates & Equilibrium Flashcards
What is RATE OF REACTION?
a measure of how fast a reactant is used up or how fast a product is formed.
What is the general pattern of rate of reaction ?
- Rate is fastest at start as each reactant is at its highest concentration.
- Slows down as reaction proceeds because reactants being used up and conc decreases.
- when one of the reactant has been completely used up the rate of reaction is 0 as reaction stops.
What 4 things affect rate of reaction?
1) Catalyst
2) Surface area of reactants
3) temperature
4) concentration or pressure for gases
Describe the collision theory.
two reacting particles must collide with correct orientation and sufficient energy to overcome activation energy for a reaction to occur.
How does increasing CONCENTRATION affect the ROR?
increasing conc increases the number of particles in the same volume so particles are closer together and colliding more frequently so more successful collisions in a given time.
How does increasing PRESSURE affect the ROR?
Increasing pressure means more particles in a smaller volume so collisions are more frequents so more successive collisions in a given time.
What are 2 ways of measuring the progress of a reaction to measure the rate?
1) monitor the removal of reactant
2) or formation of a product
When do you know a reaction is complete when monitoring a reaction that produces gas by weighing it?
When no more gas is produced so there is no change in scale reading.
What are catalysts?
a substance that changes the rate of reaction without undergoing any permanent change by providing a route with a lower activation energy.
What are HOMOGENOUS catalysts?
catalysts that has same physical state as reactants.
they work by reacting with reactants to form intermediate that then breaks down to give the product and regenerates the catalyst.
What are HETEROGENOUS catalysts?
catalysts with different physical state as reactants.
tend to provide a surface for the reaction to take place.
reactant molecules are ABSORBED onto the surface and products leave through DESORPTION.
How are catalysts sustainable and economical?
- less need for energy so reduces temp - less fossil fuels and so less emissions of carbon dioxide.
- cuts cost of energy so more profit.
What is on the axes of a boltzmann distribution?
y axis - number of molecules with a given energy.
x axis - energy
What are the 3 main features about a boltzmann distribution?
1) starts at zero because no molecules = no energy.
2) Area under curve equals the total number of molecules.
3) no maximum energy for a molecule so curve never meets x axis.
What happens to the boltzmann distribution when the temperature is increased?
- area stays the same
- more molecules with higher energy so height decreases and peak shifts slightly to right.
- more molecules with equal to or greater than activation energy
What happens to boltzmann distribution when catalysts are added?
The activation energy shifts to left so more molecules have energy equal to or greater than the lowered activation energy.
What are the 2 features of an equilibrium system?
1) rate of forward reaction is equal to the rate of reverse reaction.
2) concentrations of reactant and products do not change.
Why does a reaction need to be in a closed system to remain in equilibrium?
So that temperature, concentrations of reactants and products are unaffected by outside influences.
What does le Chatelier’s principle state?
When a system in equilibrium is subjected to external change, the system readjusts itself to minimise the effect of that change.
Which way does the equilibrium move when concentration changes?
Moves towards the higher concentration.
more products, shifted to right.
Which way does equilibrium move when temperature changes?
INCREASE in temp shifts equilibrium towards endothermic reaction.
DECREASE in temp shifts equilibrium towards exothermic reaction.
How does pressure affect equilibrium position?
Shifts it to the side with fewer particles (mols)
What affect does catalysts have on the equilibrium position.
NONE.
it just speeds up the rate at which the equilibrium can be reached.
How do you calculate equilibrium constant (Kc)?
[products] ÷ [reactant]
with mol no. as power.
What does the equilibrium constant tell us?
- position of equilibrium
- whether there are more reactants or products in an equilibrium system.
Kc > 1 = more reactants as equilibrium towards right
Kc
