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Hello, I am Mrs. Adcock, and welcome to today's lesson.
Today's lesson is on surface area and rate analysis.
We are going to be analysing a set of data to see the effect of surface area on the rate of reaction.
We will be using this data to work out the mean rate of reaction and the instantaneous rate of reaction.
Today's lesson outcome is "I can represent graphically and describe how the rate of reaction depends on the surface area of a solid reactant." Some of the key words we will be using in today's lesson include gradient, mean rate of reaction, instantaneous rate of reaction and tangent.
Here you can see each of those keywords written in a sentence.
It would be a good idea to pause the video now and read through those sentences.
You might even like to make some notes so that you can refer back to them in the lesson if needed.
Today's lesson on surface area and rate analysis is split into three main parts.
First of all, we are going to be calculating the mass of product produced.
Then we are going to look at how we calculate the mean rate of reaction.
And finally, we are going to be looking at calculating instantaneous rate of reaction.
Let's get started on the first part of our lesson, calculating the mass of product produced.
To determine the rate of reaction, we need to know either the amount of reactant used in a given time, and we can use this to work out the rate of reaction by calculating the amount of reactant used divided by the time taken.
Or we need to know the amount of product made in a given time.
And we can use this to calculate the rate of reaction by doing the amount of product made divided by the time taken.
"If a reaction produces a gas, we can measure the decrease in mass as the gas escapes to the surroundings in a given time." And the equipment could be set up as follows.
We've got a mass balance.
We have our reaction vessel on top of the mass balance, and for this reaction we have marble chips and acid in the conical flask, and we can use this equipment to measure the decrease in mass as a gas is produced and escapes to the surroundings.
"We can calculate the mass of product made in grammes from data on the decreasing mass of a reaction mixture." Here we have an experiment.
And initially, at where the time is zero seconds, the reaction vessel has a mass of 150.
0 grammes.
After 30 seconds, so when the time is 30 seconds, the mass of the reaction mixture is 149.
4 grammes.
So there has been a decrease in mass of the reaction mixture.
And we can use this to help us calculate the mass of product that has been made.
In this reaction, after 30 seconds, the reaction mixture has decreased from 150.
0 grammes to 149.
4 grammes.
So the mass of gas that has been produced and escaped to the surroundings is 150.
0, so the initial mass of the reaction mixture minus 149.
4 grammes.
And this gives us a mass of 0.
6 grammes.
So 0.
6 grammes of product was made and escaped to the surroundings.
"To calculate the mass of gas that's produced, we deduct the mass of the reaction mixture from the initial reaction mixture at zero seconds." Here we have a table of results, and we have the mass of the reaction mixture where we used calcium carbonate chips in grammes and the mass of that reaction mixture was recorded every 30 seconds.
So we can see initially, the reaction mixture had a mass of 150.
0 grammes.
After 30 seconds, it had decreased to 149.
4 grammes.
By 60 seconds, it had decreased to 148.
8 grammes.
And by 90 seconds, the reaction mixture had decreased to 148.
3 grammes.
So we can work out the mass of carbon dioxide produced.
At the beginning, when time equals zero, no mass of product has been produced, so the mass of carbon dioxide produced is zero grammes.
After 30 seconds, the reaction mixture has decreased from 150 to 149.
4 grammes.
So if we deduct the reaction mixture from the initial reaction mixture, we can work out the mass of gas produced, and this will be 0.
6 grammes.
After 60 seconds, again, we have deducted the reaction mixture from the initial reaction mixture and we have a mass of 1.
2 grammes.
And again, we have done the same after 90 seconds.
So we have deducted the mass of the reaction mixture at 90 seconds from the initial reaction mixture, and this tells us that we have produced a mass of 1.
7 grammes of gas.
"A reaction mixture has an initial mass of 150.
0 grammes.
After three minutes, the reaction mixture mass is 148.
0 grammes.
What mass of gas has been produced?" Is it A.
8.
0 grammes? B.
3.
0 grammes? Or C.
2.
0 grammes? The mass of gas that has been produced is 2.
0 grammes.
We deduct the reaction mixture at three minutes, which is 148.
0 grammes from the initial reaction mixture, which was 150.
0 grammes.
And that tells us the mass of gas produced was 2.
0 grammes.
Well done if you correctly calculated that answer.
Time for our first practise task of today's lesson.
You need to use the data to calculate the mass of product made when the calcium carbonate chips were reacted with hydrochloric acid.
Pause the video now, have a go at answering this question, then come back when you're ready to move on.
Here you can see the mass of carbon dioxide that has been produced for each of those time intervals.
Hopefully, you got those correct.
If you made any mistakes, then remember you just need to deduct the mass of the reaction mixture at each of those time periods from the initial mass of the reaction mixture.
For question two, you need to use the data to calculate the mass of product made.
But this time, when the calcium carbonate was a powder and this reacted with hydrochloric acid.
Pause the video now and have a go at completing this table.
Let's see if you calculated those masses correctly.
You can see they are given there to you in the bottom row.
So just check carefully if you have calculated the mass of carbon dioxide produced correctly.
For the final part of this practise task, you need to plot a graph.
And your graph is going to have the mass of carbon dioxide produced in grammes against time in seconds.
For the reactions with the calcium carbonate chips and powder you should end up with one graph, have your time on the x-axis, and the mass of carbon dioxide produced in grammes on the y-axis.
You will plot both sets of data for the calcium carbonate chips and for the powder on the same graph.
Pause the video now and come back when you have finished your graph.
Your graph should look similar to this one here where we have the mass of carbon dioxide produced in grammes on the y-axis.
We have the time in seconds on the x-axis.
And we have a curve that represents the calcium carbonate powder and a curve for the calcium carbonate chips.
Well done if you have correctly drawn your graph.
We have had a look how we can calculate the mass of products produced from data on the decreasing mass of a reaction mixture.
We're now going to move on to have a look at how we can calculate the mean rate of reaction.
"Graphs of mass, volume, or concentration versus time can show how the rate changes throughout a chemical reaction." Here we have a graph of the volume of carbon dioxide made, and this has been measured in centimetres cubed.
And we have the time in seconds.
The gradient on this graph represents the rate of reaction.
And the steeper the slope, the greater the rate of reaction.
So the gradient starts off steep in this reaction and slowly becomes shallower until the reaction has ended.
So we know initially there is a high rate of reaction and the rate decreases as the reaction progresses.
We can interpret graphical data to understand what happens to the rate over the course of most reactions.
Here we can see the gradient is steepest.
The rate of reaction is highest at the start of a reaction.
The rate of reaction slows down as the reaction progresses.
How can we tell this? Well, we can see that the gradient becomes shallower as the reaction progresses.
Eventually, the curve levels out and the rate of reaction is zero because the reaction has ended.
When reacting excess calcium carbonate with acid, the same volume of gas is produced regardless of the surface area.
Here we've got the mass of carbon dioxide produced in grammes and the time in seconds.
And we have a set of data for powder and for calcium carbonate chips.
And we can see the final mass of carbon dioxide produced for the powder and chips is 3.
0 grammes.
So we produce the same volume of gas even when we change the surface area.
The surface area affects the rate of reaction and doesn't impact the volume of gas produced, so long as we were reacting excess calcium carbonate with acid.
If the calcium carbonate is in excess, then it is the acid that is the limiting reagent and this is controlling the volume of products that is made.
Therefore, the volume of product made stays the same when we change the surface area of the calcium carbonate.
It is only the rate of reaction that will change for different surface areas.
When we have the powder, we have a higher rate of reaction, and we produce that final mass of carbon dioxide in a shorter time.
Time for a question.
Is this statement true or false? 10 grammes of a metal carbonate powder will react with acid to produce a higher mass of product compared to 10 grammes of metal carbonate chips.
And the metal carbonate is in excess in this reaction.
That statement is false.
So well done if you got that correct.
Can you all now try and explain why this statement is false? This statement is false because "The final mass of product will be the same.
The powder will produce the product at a faster rate as it has a larger surface area than the chips." Because the metal carbonate is in excess, when we use 10 grammes of metal carbonate powder or 10 grammes of metal carbonate chips, we will produce the same mass of product, the powder will just produce that product at a faster rate.
Well done if you explained why that statement was false correctly.
"Here is a worked example calculating the mean rate of reaction for the reaction shown on the graph below." And the mean rate of reaction is the average rate at which reactants are turned into products in a given time.
On the graph below, we can see the volume of carbon dioxide made in centimetres cubed and the time in seconds.
Now to work out the mean rate of reaction, we are going to look at the total volume of product that has been made.
And in this reaction, the total volume of carbon dioxide made is 60 centimetres cubed.
The reaction takes 70 seconds to reach completion.
So we have looked at the amount of product made and the time taken.
We can then work out the mean rate of reaction by calculating the amount of product made divided by the time.
So this will be 60 centimetres cubed divided by 70 seconds, and this gives us a mean rate of reaction of 0.
86 centimetres cubed per second.
"What will we work out if we calculate the total volume of gas produced divided by the total time of reaction?" A.
The initial rate of reaction.
B.
The mean rate of reaction.
Or C.
The instantaneous rate of reaction.
The correct answer is B.
The mean rate of reaction.
So well done if you've got that question correct.
Time for our second practise task of today's lesson.
Question one.
"Calculate the mean rate of reaction for the reaction using the chips." You can see we have a graph there of the mass of carbon dioxide made in grammes and the time in seconds.
You need to use this graph to calculate the mean rate of reaction.
Pause the video now, have a go at answering this question, then when you come back, we'll go over the answer.
To calculate the mean rate of reaction, we need to first of all, work out the total mass of product made.
And the total mass of carbon dioxide made in this reaction was 3.
0 grammes.
The time taken for this reaction to reach completion is 275 seconds.
You may have an answer of somewhere between 265 to 275 seconds.
To work out the mean rate of reaction, we do the total mass of product made, which is 3.
0 grammes divided by the time taken, which is 275 seconds, and that gives us a mean rate of reaction of 0.
011 grammes per second.
Well done if you calculated that correctly.
Remember to always show your workings on the graph.
For question two, you need to calculate the mean rate of reaction for the reaction using the powder.
Again, we have the mass of carbon dioxide made in grammes and the time in seconds.
So pause the video now and calculate the mean rate of reaction for the reaction using the powder.
When you come back, we'll go over the answer.
Let's see how you got on.
So the total mass of carbon dioxide made is the same as when we used the calcium carbonate chips, so it's 3.
0 grammes.
However, this reaction was completed in a shorter time because we had a larger surface area.
So the time for the reaction to reach completion is about 150 seconds.
You may have a reading of somewhere between 140 and 150 seconds.
Therefore, the mean rate of reaction is the total volume of product made divided by the time taken, which is 3.
0 divided by 150, and that gives us an answer of 0.
020 grammes per second.
Or you might have 0.
021 grammes per second if you used a different time.
We have had a look at calculating the mass of product produced, and how we can analyse graphs to calculate the mean rate of reaction.
Now we are going to move on to have a look at how we can calculate the instantaneous rate of reaction.
"The instantaneous rate of reaction is the rate of reaction at a specific time in the reaction." So this is different to the mean rate of reaction, which is the average rate over the time of the reaction.
The instantaneous rate of reaction can be determined from the gradient of the curve at a specific time.
And to calculate the instantaneous rate of reaction, from a graph at a specific time, we first of all, need to draw a tangent to the curve, and then secondly, calculate the gradient of the tangent.
And we can calculate the gradient by doing the change in y divided by the change in x.
"Here is a worked example calculating the instantaneous rate of reaction at 20 seconds for the reaction shown on the graph below." We have the volume of carbon dioxide made in centimetres cubed and the time in seconds.
First of all, we are going to identify where 20 seconds appears on the graph, because we are going to work out the instantaneous rate of reaction at 20 seconds.
You can see 20 seconds marked there with an X.
Then we are going to draw a tangent at time equals 20 seconds.
A tangent is a straight line that touches the curve at a point.
Our tangent touches the curve at time equals 20 seconds.
You will need to use a ruler to draw your tangents.
Then we need to calculate the gradient of the tangent line.
So we are going to use change in y divided by change in x.
If we have a look at our change in y, change in y goes from 150 centimetres cubed down to zero centimetres cubed.
So this will be 150 minus zero, which is 150 centimetres cubed.
Our change in x is 60 seconds minus zero seconds, and this gives us a change in x of 60 seconds.
Then to calculate the gradient at 20 seconds, we do change in y divided by change in x.
So this is 150 centimetres cubed divided by 60 seconds, which gives us a gradient of 2.
5 centimetres cubed per second.
And this tells us that the rate of reaction at 20 seconds is 2.
5 centimetres cubed per second.
Is this statement true or false? "To calculate the instantaneous rate of reaction, we draw a tangent and calculate the gradient of the tangent line using change in x divided by change in y." Read over that statement carefully and decide whether you think it is true or false.
That statement is false.
Can you now explain why that statement is false? To calculate the instantaneous rate of reaction, we do draw a tangent and then we calculate the gradient of the tangent.
So that part was all correct.
However, to calculate the gradient, we use change in y divided by change in x, not change in x divided by change in y.
"A higher rate of reaction means that more reactant is used or more product made in a given time.
The following data shows the instantaneous rate of reaction at 100 seconds.
for the calcium carbonate chip and powder." We can see the calcium carbonate reactant we used.
So in one reaction we used the chips, and in another reaction we used powder.
And we can see the rate of reaction at 100 seconds in grammes per second.
So the chips had a rate of reaction of 0.
0088 grammes per second, and the powder had a rate of 0.
0100 grammes per second.
"A higher mass of carbon dioxide is produced per second for the powder compared to the chips." The powder, which has a larger surface area, had a higher instantaneous rate of reaction at 100 seconds.
Time for a question.
"Which reaction produces product at a higher rate?" Is it A.
Reaction one, which has a rate of 0.
01 grammes per second? B.
Reaction two, which has a rate of 0.
02 grammes per second.
Or C.
Reaction three, which has a rate of 0.
03 grammes per second.
We want to know which reaction produces product at a higher rate.
The correct answer is C.
So well done if you chose answer C.
Reaction three has a higher rate of reaction, and we know this because it is producing 0.
03 grammes per second.
So it is producing more product per second.
Time for our final practise task of today's lesson.
Question one.
"Calculate the instantaneous rate of reaction at 100 seconds for the reaction using the chips." You've been given the data there.
You have the mass of carbon dioxide made in grammes and the time in seconds.
Remember when we are calculating the instantaneous rate of reaction, you need to draw a tangent, and you need to calculate the gradient of the tangent.
Good luck answering this question.
Pause the video now and then come back when you're ready to go over the answer.
Let's have a look if you answered this question correctly.
So hopefully, you identified where 100 seconds was on the curve.
And then you should've drawn a tangent at 100 seconds.
So your tangent is a straight line that touches the curve at this point.
We then calculate the gradient of the tangent line by using the equation change in y divided by change in x.
For the tangent I have drawn here, the change in y will be 3.
25 minus 1.
5, which gives us a value of 1.
75 grammes.
And the change in x is 200 minus zero, which is 200 seconds.
The gradient of the tangent line is therefore 1.
75 divided by 200, which gives us an answer and an instantaneous rate of reaction at 100 seconds of 0.
0088 grammes per second.
Your tangent line may be drawn slightly differently, but you should have a very similar value for your instantaneous rate of reaction.
Question two is to calculate the instantaneous rate of reaction, again, at 100 seconds.
And this time, for the reaction using the powder.
You have a graph which has the mass of carbon dioxide made in grammes and the time in seconds.
So pause the video now, calculate the instantaneous rate of reaction at 100 seconds for this reaction using the powder, then come back when you're ready to have a look at the answer.
How did you get on? Hopefully, you've identified 100 seconds on the chart and drawn a tangent at time equals 100 seconds.
Then we calculate the gradient of the tangent line.
We can see here the change in y for the tangent line drawn here is 3.
25 minus 1.
75, which is 1.
5 grammes.
And the change in x is 150 minus zero, which is 150 seconds.
So the gradient of the tangent line will be 1.
5 grammes divided by 150 seconds, which gives us an answer of the instantaneous rate of reaction at 100 seconds of 0.
010 grammes per second.
And again, you may have drawn your tangent line slightly differently and therefore, your values will be different, but overall, you should still get a very similar value for the instantaneous rate of reaction at 100 seconds.
For the final part of this task, you need to use the information in the table to describe what effect surface area has on the rate of reaction.
We have a column which tells us the calcium carbonate reactant used, whether it was chips or powder, and we have the mean rate of reaction here for these reactions.
Use this information to see if finally, we can conclude as to what effect surface area has on the rate of reaction.
Pause the video now, answer this question, then when you come back, we'll go over the answer.
Your answer may include, "When the powder reacted with acid, it produced a higher mass of carbon dioxide per second.
The rate for the powder was 0.
09 grammes per second higher than the chips.
The powder has a larger surface area than the chips.
Therefore, the larger the surface area, the higher the rate of reaction." Well done if you got that question correct.
Hopefully, you were able to identify that the powder had a larger surface area, and you've used the data in your answer.
We have reached the end of today's lesson on surface area and rate analysis.
Well done for all your hard work throughout today's lesson.
Let's just summarise some of the key points that we have covered in today's lesson.
The changing rate of a chemical reaction can be represented by a graph of mass of gas produced, or volume of gas produced against time.
When reacting excess marble chips with acid, the same mass or volume of gas is produced for all surface areas of chips.
And we can calculate the mean rate of reaction by taking the total mass or volume of gas produced and dividing that by the time taken for the reaction.
"The instantaneous rate of reaction is equal to the gradient of the graph.
The gradient of a rate of reaction graph can be calculated from a tangent drawn at a point on the curve." Thanks for joining me for today's lesson.
I hope that you've enjoyed it, and that you're able to join me for another lesson soon.
