Draw your own tangents on gas and mass curves, find the initial rate, compare rates at two times and give a rate in mol/s.
What you will learn
- Draw a tangent at a given time and find its gradient
- Find the initial rate from a tangent at 0 s
- Give a rate from a falling mass curve
- Convert a rate in cm³/s to mol/s
Drawing a tangent yourself
A tangent touches the curve at one point and has the same steepness as the curve there.
On a paper you draw it yourself, so the mark scheme accepts a range of answers.
- Mark the point on the curve at the time you are given
- Lay a ruler so it touches the curve only at that point, not cutting through it
- Draw a long straight line: the longer it is, the more accurate the gradient
- Pick two points on the line far apart, where they cross gridlines if you can
- rate = change in volume ÷ change in time, using those two points
- Tangent at 25 s through (0, 13.2) and (50, 50.0)
- gradient = (50.0 − 13.2) ÷ (50 − 0) = 36.8 ÷ 50
- rate at 25 s = 0.74 cm³/s
The rest of this lesson and its 7 practice questions are locked.
In this lesson
- Drawing a tangent yourself
- The initial rate
- Falling curves and moles
7 practice questions, marked as you go; about 25 minutes in all.
Key terms
Initial rate, Falls
In this unit: Rates of reaction and equilibrium
Measuring and graphing rates, collision theory and the factors that change a rate, the rates required practical, reversible reactions and how conditions move an equilibrium.