P2 - 6.3 Measuring Rates of Reaction from a Graph Flashcards
The Rate of Extent of Chemical Change
What are the 2 equations to find the rate of reaction
Rate of reaction = quantity of products used/time taken
Rate of reaction = quantity of reactants used/ time taken
If this reaction produced 1200cm^3 of hydrogen in 4 minutes what is the rate of reaction
Mg + 2HCl -> MgCl2 + H2
Rate of reaction = quantity of products formed/ time taken
4x60 = 240s
Rate of reaction = 1200cm^3 / 240
Rate of reaction = 5cm^3/s
Why are rate of reaction equations not always accurate
- it is just an average
- reactions are quicker at the beginning
- reactions slow over time
- reactions may have finished by the time it says
How can we see how the rate of reaction changes throughout the reaction
Plot it on a graph
What goes on the x axis of a rate of reaction graph
Time (minutes or seconds)
What would go on the y axis of a rate of reaction graph if we were looking at the product of how much hydrogen was produced
Volume of hydrogen produced
In this reaction:
Mg + 2HCl -> MgCl2 + H2
Why does the graph start with a very steep curve
There is lots of magnesium and acid that can react together to produce lots of hydrogen
If a rate of reaction is steep what can we tell about the rate of reaction
Rate of reaction is high
What is meant when a graph plateaus
The line becomes flattened
What happens when a rate of reaction graph becomes less steep
There is less reactants left so its a much slower rate of reaction
What happens when a rate of reaction graph plateaus
One or both of the reactants is completely used up so it can no longer react and stops
How do we calculate the mean rate of reaction on a rate of reaction graph
1) draw a line from the time given and then across to the y axis
2) whatever the y axis is divide that by the time given to get an average
What is the mean rate of reaction in the first 3 minutes?
(Y axis is 1200cm^3)
3 x60 = 180s
1200/180 = 6.67cm^3/s
How do we calculate the actual rate at a particular time on a rate of reaction graph
1) Draw a line from the time given until it intersects
2) draw a tangent from the curve ( a straight line that touches the curve and has same gradient of curve at that point)
3) find gradient of tangent using change in y/change in x -> change in volume/change in time
4) draw tangent to touch y axis and join the end to the x axis and y axis
5) work out the numbers and put into second equation
What is the actual rate of reaction at 2 minutes
Draw a line from 2 mins until it reaches curve and draw a long tangent and create a box at the end
Work out distance in change of y axis and x axis
600/ 2 mins 50s (170s)
= 3.53cm^3/s
