Rates Flashcards
equation for rate of reaction
mean rate of reaction =
quantity of reactant used
/time taken
mean rate of reaction =
quantity of product formed/
time taken
plot the quantity of product formed over time (on a graph)
https://bam.files.bbci.co.uk/bam/live/content/zbwngk7/medium
https://bam.files.bbci.co.uk/bam/live/content/zbwngk7/medium
what does the gradient/slope of the line show
The slope of the line gives us an idea of the rate of reaction.
The steeper the slope, the faster the reaction
https://bam.files.bbci.co.uk/bam/live/content/zbwngk7/medium
describe what is happening over the course of the reaction
Initially, the reaction is very fast.
A lot of product is being made/formed in a short amount of time
This is because there are a large number of reactant molecules so lots of them are reacting and forming the product
Gradually the slope of the line is becoming less steep
This shows us that the reaction is slowing down, the rate of the
reaction is decreasing
That is because a lot of the reactant molecules have already reacted and turned into products
This means that there are fewer reactant molecules available to react.
At the end, the slope of the line is now zero. The line is flat. At this point the reaction has stopped. All of the reactant molecules have already reacted.
if product was a gas, then what would you measure the quantity in
cm^3
plot the quantity of reactant used over time (on a graph)
https://mmerevise.co.uk/app/uploads/2023/01/mass-of-reactant-1024x676.png
describe what is happening over the course of the reaction
https://mmerevise.co.uk/app/uploads/2023/01/mass-of-reactant-1024x676.png
Initially, the reaction is very fast.
A lot of reactant is being used in a short amount of time
This is because there are a large number of reactant molecules so lots of them are reacting and forming the product
Gradually the slope of the line is becoming less steep
This shows us that the reaction is slowing down, the rate of the
reaction is decreasing
That is because a lot of the reactant molecules have been used and have already reacted and turned into products
This means that there are fewer reactant molecules available to react.
At the end, the slope of the line is now zero. The line is flat. At this point the reaction has stopped. All of the reactant molecules have been used and have already reacted.
In a chemical reaction, 60g of product was formed in 15s.
Calculate the mean rate of reaction
mean rate of reaction =
quantity of product formed/
time taken
= 60/15 = 4g/s
20g of product was formed in 40s, in a chemical reaction
Calculate the mean rate of reaction
mean rate of reaction =
quantity of product formed/
time taken
= 20/40 = 0.5g/s
20g of product was formed in 40s, in a chemical reaction
The mean rate of reaction is 0.5g/s what does this mean
This means that 0.5g of the product is being formed every second
30g of reactant was used in 10s
Calculate the mean rate of reaction
mean rate of reaction =
quantity of reactant used
/time taken
= 30/10
= 3 g/s
30g of reactant was used in 10s
What does this mean
This means that 0.5g of the reactant is being used every second
calculate the mean rate of reaction after 20s using the graph
mean rate of reaction =
quantity of product formed/
time taken
Using the graph, find out the total volume of gas produced after 20s
go up from 20, hit the graph then go horizontally to the y - axis and read the value
then substitute in values
On a rate of reaction graph, the slope of the curve is constantly changing. what does this mean
The slope of the curve is constantly changing.
This tells us that the rate is also constantly changing (the amount of product formed, at every second is constantly changing)
This makes it very difficult to get a clear idea of the rate of reaction at any specific point
calculate the rate of the reaction at 20s - use the graph
Draw a line going up from 20 hitting the curve
Draw a tangent on the curve, which just touches that point
Make sure the gaps on either side are equal
Calculate the gradient of the tangent using the equation change in y/change in x
change in y = 48cm3 -28cm3 = 20 cm3
change in x = 34 s - 10s = 24 s
gradiuent = 20/24 = 9.83 cm3/s
draw lines from change in y and changin x to the axes to show working out
what does the slope/gradient of the tangent show
the slope of the tangent gives us an idea of the rate of reaction
(this tangent has a steeper slope than the tangent later in the reaction) - this tells us that the reaction is faster at the start than towards the end
factors affecting the rate of reaction
concentrations of reactants in solution, the pressure of reacting
gases, the surface area of solid reactants, the temperature and the
presence of catalysts.
Describe and explain the effect of the concentration of reactants on the rate of reaction
If the concentration of reactants increases, the particles become more crowded (there are a greater number of particles in a given volume)
the particles collide more frequently
so there will be more frequent successful collisions
so rate of reaction increases
Describe and explain the effect of the pressure of reacting gases on the rate of reaction
If the pressure of reacting gases increases, the particles become more crowded (there are a greater number of particles in a given volume)
the particles collide more frequently
so there will be more frequent successful collisions
so rate of reaction increases
what is collision theory
Collision theory states that chemical reactions can only take place when the reacting particles collide with each other
The collisions must have sufficient energy
what is the rate of a chemical reaction dependent on/determined by
The rate of a chemical reaction is determined by the frequency of successful collisions
(frequency means number of successful collisions per second)
explain the shape of the graph using collision theory
https://bam.files.bbci.co.uk/bam/live/content/zbwngk7/medium
Reactions are rapid initially because we have a large number of reactant molecules
This means that we have a large number of collisions per second
Over time, reactions slow down, because the number of reactant molecules is running out
That means that there are a smaller number of collisions per second
Finally the reaction stops because all of the molecules have run out
This means that the number of collisions per second is now zero
rate of reaction is ______ to the concentration
proportional
Describe and explain the effect of the temperature of the reactants
If temperature is increased
the reactant particles move faster ( have more kinetic energy)
particles collide more frequently
and more particles have the activation energy
so more frequent successful collisions so the rate of reaction is increased
Describe and explain the effect of the surface area of the solid reactants
if the solid reactant is broken into small pieces or ground into a powder (smaller particle size = bigger SA)
If the surface area of the solid reactants increased
its surface area increases
more solid particles are exposed to the reactant
meaning there are more frequent collisions
there are more frequent successful collisions
so rate of reaction increases
Describe and explain how the presence of a catalyst effects the rate of reaction
A catalyst works by providing a new pathway for the reaction with a lower activation energy
So with a catalyst, more particles will have enough (the required) energy to react, so rate of reaction increases
(lower activation energy means higher rate)
give one reason why using a catalyst reduces cost
Using catalysts speed up the reaction and you can lower tempeature for reaction
Catalysts speed up chemical reactions which means more products are produced in the same amount of time which means products are cheaper
investigating temperature and rate of reaction
As temp. increases the rate of reaction increased
As temp increased the steepness of the line increased on the graph also increased meaning that the rate of reaction increased
as the conc. of sodium thiosulfate solution doubles, the rate of reaction doubles
explain this
As the conc. of sodium thiosulfate doubles ( meaning as the amount of particles in a given volume double), the reactivity doubles (this is because when the number of particles in a volume doubles, the number of particles increased meaning there were more frequent collisions. This causes there to be more frequent successful collisions, meaning the rate of reaction is higher)
what do enzymes act as
Enzymes act as catalysts in biological systems.
https://www.elevise.co.uk/uploads/9/8/0/2/98021560/published/screenshot-2020-12-31-at-16-48-15_3.png
look at blue and green line
blue line - higher conc of reactant
orange line - lower conc. of reactant
explain why the lines look different and how they relate to rate of reaction
The higher concentration is a faster reaction.
We can tell that because the line is steeper
With the higher concentration get more product at the end,
This is because we started with more reactant molecules at the start (higher conc. = more reactant particles in a given volume)
