Calculating the Rate of Diffusion Flashcards

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What does 'rate of diffusion' mean in calculations?

How much of a substance moves in a given time. Rate = change in amount ÷ time.

How do you calculate rate when you measure distance moved?

Rate = distance ÷ time. Example: 2.0 cm in 40 s gives 0.050 cm/s.

What units can be used for rate of diffusion?

Use units that match what you measured. Examples: cm/s for distance, mg/min for mass, cm3/s for volume.

How do you convert minutes to seconds before calculating a rate?

Multiply the number of minutes by 60.

How do you calculate a mean rate from repeat results?

Find the rate for each repeat. Then mean rate = sum of the rates ÷ number of repeats.

What is the rule that links rate with surface area, concentration difference and diffusion distance?

Rate is proportional to surface area × concentration difference ÷ diffusion distance.

If surface area doubles and everything else stays the same, what happens to the rate?

The rate doubles.

If diffusion distance (membrane thickness) doubles, what happens to the rate?

The rate halves.

If the concentration difference is three times bigger, what happens to the rate (all else the same)?

The rate is three times bigger.

How do you compare two setups using the rule for diffusion rate?

For each setup, do surface area × concentration difference ÷ diffusion distance. The bigger value is faster.

How do you find a rate from a straight-line graph of amount or distance against time?

Find the gradient. Rate = change in y ÷ change in x.

How do you find the concentration difference across a membrane?

Subtract the lower concentration from the higher one. Use the same units.