reaction rates Flashcards
What does rate of chemical reaction measure
how fast a reactant is being used up or how fast a product is being formed
Rate of reaction equation
change in concentration / time
Amount of reactant used or product made / time
Why is rate of reaction fastest in the beginning
each reactant is at its highest concentration
Factors that change rate of reaction
Temp
Catalyst
surface area
concentration
What does collision theory state
for reaction to occur
particles must collide
particles must have sufficient energy - kinetic energy
Particles must collide with the correct orientation
How is enthalpy change measured in a graph
products to reactants
How can you show effect of SA to the rate of reaction
reacting marble chips with acid. The carbon dioxide gas evolved can be collected and its volume measured over time. Repeat with marble chips of different size
Effect of temperature on rate
higher total no of collisions means higher no of successful collisions
Higher activation energy, higher proportion of collisions successful
Activation energy meaning
The minimum energy needed for a chemical reaction to happen
Where is the activation energy in an energy profile
Between reactants and top of the profile
What does a Maxwell-Boltzmann Distribution show
The energy in gas particles
Do particles of a gas in sample move at the same speed
Move at a different speed
Have a different amount of kinetic energy
What does the highest peak of the Maxwell-Boltzmann Distribution mean
The most likely energy of a particle in a sample
What does the line to the right of the highest peak mean
The mean energy particles have
What does the area under the graph mean
Total number of molecules
How does increasing pressure increase rate
Particles are closer together - collide more often
More frequent collisions
Higher chance of collision
How does increasing concentration increase rate
Particles are closer together
What is a catalyst
Substance that increases the rate of reaction by providing an alternative pathway that has lower activation energy. Chemically unchanged. More molecules exceed activation energy
What are the 2 types of catalysts
Homogeneous and Heterogeneous
Heterogeneous catalyst
Different state to the reactants
Homogeneous catalyst and what they form
Same state as the reactants
Forms intermediate species by reactants combining with the reactants to form the products.
Catalyst is reformed again
4 reasons catalysts are used in the industry
Lower temp - less co2 produced
Speed up a reaction by providing an alternative pathway
Change the property of a product
Reduce the use of toxic reactants
Example of a reversible reaction
Haber process
making ammonia
NH3
Characteristic of an equilibrium system
Rate of forward reaction = rate of backward reaction
The concentration of product or reactant do not change
In a closed system
What does le chateliers principle state
When there is an external change to a system in equilibrium, the reaction tries to minimise the change
What does an increase in the concentration of reactants lead the equilibrium system to do and in what situation?
Shifts to the opposite direction
Only works in homogenous equilibria (same state)
what happens if we increase the pressure in equilibria
shifts to the side with fewest moles and vice versa
What happens if we increase the temp in equilibria
Shifts to the endothermic side vice versa
What does a catalyst do to the equilibria
No effect on the position - has no effect on the yeild
speed up the rate of reaction equally
What is the pressure, temperature, catalyst for making ethanol?
60 atmospheres
300 degrees
phosphoric acid
How does lowering the temperature to make ethanol lead to a compromise?
Equilibrium shifts to the right
However, lower temp means lower rate of reaction.
300 degrees is a compromise between yield and rate
How does increasing the pressure to make ethanol lead to a compromise?
High pressure would increase the rate and shift to the right
But are expensive because thicker pipes are needed.
What does Kc tell you
Calculate equilibrium constants
Indicates whether there are more products or equilibrium in the system
