Gradients, mean rates, rate as 1000 ÷ time, proportional or linear, reading lines of best fit and tangents.
What you will learn
- Calculate a rate from a gradient or two readings
- Tell a proportional graph from a linear one
- Use a tangent for the rate at one time (Higher)
Rates from graphs
mean rate = change in quantity ÷ change in time
rate at one moment = gradient of the tangent (Higher)
A straight line through the origin means directly proportional. A straight line that misses the origin is linear but not proportional.
In the disappearing cross experiment, use 1000 ÷ time as a measure of rate: a shorter time means a faster reaction.
On a loss-of-mass graph the mass falls steeply at first, then more slowly, then levels off when the reaction stops; the total mass lost is the starting mass minus the final mass. To read a value from a line of best fit, go up from the value on the horizontal axis to the line, then across to the vertical axis.
The rest of this lesson and its 9 practice questions are locked.
In this lesson
- Rates from graphs
- Try it: Watch the rate change
9 practice questions, marked as you go; about 20 minutes in all.
Key terms
Directly proportional, Linear
In this unit: Required practicals and maths skills
The skills behind every chemistry practical and calculation: units, uncertainty, titrations, graphs, the equations and planning.