10 Questions
How do catalysts affect chemical reactions?
Decrease the activation energy
What effect does increasing temperature have on the rate of a chemical reaction?
Increases the rate of reaction
Why are catalysts important in biological systems?
To provide a different pathway with lower activation energy
What happens to catalysts during a chemical reaction?
They remain unchanged and unutilized
Why do catalysts increase the proportion of particles with energy to react?
By decreasing the activation energy
Which factor does NOT affect the rate of chemical reactions?
Volume
What is the general unit for rate of reaction when measured by the amount of product formed?
$cm^3/s$
How can the rate of reaction be calculated using tangents to curves?
Find the slope of the curve at the point of interest
What does activation energy represent in chemical reactions?
The minimum energy required for reactants to form products
Increasing the surface area of solid reactants is likely to increase the rate of a reaction because it:
Increases the frequency of collisions
Study Notes
Calculating Rates of Reactions
- Rate of reaction can be measured using the amount of reactant used or product formed over time
- Rate of reaction = amount of reactant used / time or amount of product formed / time
- Quantity of reactant or product can be measured in mass (g), volume (cm³), or moles (mol)
- Units of rate of reaction may be given as g/s, cm³/s, or mol/s
Graphical Method to Find Rate of Reaction
- To find the rate of reaction graphically, draw tangents to curves and use the slope of the tangent
- Calculate the gradient of a tangent to the curve on these graphs as a measure of rate of reaction at a specific time
Factors Affecting Rates of Chemical Reactions
- Factors that affect the rates of chemical reactions include concentration, pressure, surface area, temperature, and catalysts
- Increasing concentration, pressure, and surface area increases the frequency of collisions, thus increasing the rate of reaction
- Increasing temperature increases the frequency of collisions and makes the collisions more energetic, thus increasing the rate of reaction
Collision Theory and Activation Energy
- Collision theory: chemical reactions can occur only when reacting particles collide with each other and with sufficient energy
- Activation energy: the minimum amount of energy that particles must have to react
- Increasing concentration, pressure, and surface area increases the frequency of collisions, and increasing temperature makes the collisions more energetic, thus increasing the rate of reaction
Catalysts
- Catalysts are substances that speed up chemical reactions without being changed or used up during the reaction
- Enzymes act as catalysts in biological systems
- Catalysts are not included in the equation for a reaction
- Catalysts decrease the activation energy, increasing the proportion of particles with energy to react, and provide a different pathway for a chemical reaction with a lower activation energy
Test your understanding of the rate of reactions, including how to calculate rates of reactions, measuring using the amount of product used or formed over time. This quiz includes content from Topic 6: The rate and extent of chemical change in AQA GCSE Chemistry, with a focus on higher tier material.
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