AQA · Chemistry · 8462
GCSE Chemistry: Calculating rates of reactions
The rate and extent of chemical change · AQA GCSE Chemistry (8462), specification point 4.6.1.1. Cards are generated from the exam board's own specification for "Calculating rates of reactions", and every card links back to the page it came from. Specification © AQA — used with attribution.
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How can the rate of a chemical reaction be measured experimentally?
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By measuring the quantity of a reactant used up, or the quantity of a product formed, over time.
What is the equation for the mean rate of a reaction?
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Mean rate of reaction = quantity of reactant used (or product formed) ÷ time taken.
In which two ways can the quantity of a reactant or product be measured for rate calculations?
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As a mass in grams, or as a volume in cm³.
When the quantity of reactant is measured as a mass, the rate of reaction has units of ?.
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g/s
What unit is used for rate of reaction when the product is measured as a gas volume?
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cm³/s (volume per second).
What unit is used for rate of reaction when quantity is measured in moles? (Higher Tier)
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mol/s.
A reaction produces 60 cm³ of gas in 30 s. What is the mean rate?
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2 cm³/s (60 cm³ ÷ 30 s).
Which two variables are plotted on a graph used to find the rate of a reaction?
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Quantity of product formed (or reactant used) on the y-axis against time on the x-axis.
How is the rate of reaction at a specific time found from a curved quantity–time graph?
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Draw a tangent to the curve at that time; the gradient (slope) of the tangent is the rate at that moment.
Why must a tangent be drawn to find the rate at a particular time on a curved graph?
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Because the rate changes over time, so the curve's gradient is not constant; the tangent's slope gives the rate at that instant.
On a graph of product formed against time, the ? of the line is a measure of the rate of reaction.
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gradient
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