Rates of reaction Flashcards
What are the factors that affect the rate of reaction
Temperature
Pressure
Catalyst
Surface area
Concentration
What does the rate of reaction mean
The change in concentration between the reactants and products overtime
What are the units for concentration
moldm-3s-1
What is the collision theory
In order to react particles must collide with eachother
How should particles collide to make it successful
Must have the correct orientation and must have energy equal to or greater than the activation energy
What happens when we increase the concentration for rate
When we increase the concentration more particles are in the same unit of volume. This will mean more frequent collision occur. This means more successful collisions occur so the rate of reaction increases
What happens when we increase the pressure for rate
When we increase the pressure the same number of particles occur in a smaller volume. This means more frequent collisions occur per unit time hence more successful collisions occur. This means the rate of reaction will increase
What happens when we increase the temperature for rate
Most collisions are not successful. This is because they do not have the activation energy. However when we increase the temperature more particles will have energy equal to or greater than the activation energy so more successful collisions occur per unit time
If a reaction produces gas what are two ways of reducing the rate
1) Measuring the change in volume or pressure of gas over time
2) The loss in mass of reactants over time
What does the rate equal
To the gradient of a concentration time graph
Why is volume/time the same as concentration/ time
They are proportional
How can you state how the rate changes during the course of a reaction for concentration/time
Initially the gradient is at its steepest so the rate is highest. Overtime however the gradient becomes smaller so the rate decreases. Towards the end the curve flattens which means the gradient becomes 0 and the reaction stops
How can you explain why the rate changes with a concentration time graph
Initially the reactants are high and collision frequency is high so there are lots of successful collisions leading to a higher rate. As reactants get used up the concentration decreases which decreases collision frequency therefore the rate. At the end, one of the reactants is completely used up so the reaction stops.
What does the position of the curve depend on
The moles
What does the steepness of the curve depend on
The concentration
How do you draw a tangent at a specific point
Draw a line that only just touches the point where asked
Draw a triangle where it matches
Do change in y over change in x
How do you work out the initial rate
Draw a line at the beginning of the graph and do change of y over change of x
What does a Boltzmann curve show
The distribution of kinetic energy across all particles. Particles dont all have the same energy
How do you describe a general Boltzmann curve
The area under the curve is number of particles
No molecules have 0 energy so the graph must start at the origin
There is no maximum energy as the curve never touches the y axis
The area under the curve after the activation energy shows how many particles energy and can react
What is the effect of temperature with a Boltzmann curve
At a higher temperature the area under the curve after the activation energy is larger as more particles have reacted
What is the effect of the catalyst with a Boltzmann curve
Using a catalyst the activation energy is lowered so more particles have energy
How does the catalyst increase the rate of reaction
By providing an alternate route for the reaction with a lower activation energy. This means the increases the rate of reaction without being used up
What are the benefits of catalysts
It has lower temperature and pressure so reduces energy demand, fossil fuel consumption and greenhouse gas emissions
What is a homogeneous catalyst
Have the same physical state as the reactants. This forms an intermediate with the reactants which breaks down to regenerate the catalyst
What is a heterogeneous catalyst
Have a different physical state as the reactants. The reactants are adsorbed to the catalyst surface where the reaction takes place. The products leave the surface by desorption
