Rate Graphs Flashcards

All 6 cards in this deck

What are the steps to calculate the mean rate of reaction?

e.g. 30 cm$^3$ of gas collected in 60 s

1. Find the change in volume (or mass): 30 cm$^3$
2. Divide by the time taken: $30 \div 60$
3. Mean rate = 0.5 cm$^3$ per second

What are the steps to find the rate of reaction at a given instant from a volume–time graph?

e.g. the rate at 100 s

1. Draw a tangent touching the curve at 100 s.
2. Read the vertical and horizontal differences along the tangent: e.g. 40 cm$^3$ over 100 s.
3. Rate = gradient = $40 \div 100$ = 0.4 cm$^3$ s$^{-1}$

On a graph of volume of gas produced against time, where is the rate of reaction greatest?

At the start, where the curve is steepest.

True or false? When the line on a volume of gas against time graph becomes horizontal, the reaction has finished.

True. The volume has stopped rising because a reactant has been used up.

Why does the curve on a volume–time graph become less steep as the reaction goes on?

The reactant particles are being used up, so collisions become less frequent and the rate falls.

How does the curve change if the same mass of a solid reactant is used as a powder instead of large pieces, with all other conditions the same?

e.g. magnesium ribbon replaced by magnesium powder

The curve is steeper and levels off sooner, but reaches the same final volume of gas.