Topic 5: Monitoring and Controlling Chemical Reactions - Subtopic 2: Controlling Reactions
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How can the rate of reaction be measured?
• How fast a reactant is used up • How fast a product is made
What units are commonly used for rate of reaction?
Rate of reaction can be measured in g/s (for mass changes) or cm³/s or dm³/s (for volume changes, especially with gases)
How can you measure the rate of reaction when a gas is produced?
You can measure the loss in mass over time (if gas escapes) or collect and measure the volume of gas produced over time
What is the precipitation method for measuring reaction rate?
Place a flask with reacting solutions over a cross on paper and measure the time it takes for the cross to disappear as precipitate forms (e.g., Na₂S₂O₃ + HCl reaction forming sulfur precipitate)
How do you calculate the mean rate of reaction?
Calculate the overall change in quantity (e.g., volume of gas produced) and divide by the total time taken for the reaction
How do you determine the rate of reaction at a specific point on a curve?
Draw a tangent to the curve at that point and calculate the gradient of the tangent (change in y ÷ change in x)
How does increased concentration affect reaction rate?
Increasing concentration increases reaction rate as there are more reactant particles in a given volume, leading to more frequent successful collisions
How does increased temperature affect reaction rate?
Increasing temperature increases reaction rate as particles have more kinetic energy, exceeding the activation energy more often and causing more successful collisions
What happens to reaction rate when a solid reactant’s surface area is increased?
Reaction rate increases as more surface area is exposed to the other reactant, producing a higher number of collisions per second
What is collision theory?
Collision theory states that chemical reactions occur only when reactant particles collide with sufficient energy (activation energy) to react
What is the approximate effect of a 10°C temperature increase on reaction rate?
For aqueous and gaseous systems, a 10°C temperature increase approximately doubles the reaction rate
What is a catalyst?
A substance that speeds up the rate of a reaction without being altered or consumed in the reaction
How do catalysts affect activation energy?
Catalysts lower the activation energy by providing an alternative reaction pathway, allowing more particles to have enough energy to react
Name three important industrial catalysts
Iron (Haber Process), Vanadium(V) oxide (Contact Process), Manganese(IV) oxide (hydrogen peroxide decomposition)
What are enzymes?
Biological catalysts that control reactions in cells and biological systems
What is an advantage of using enzymes in industrial processes?
Enzymes allow industrial reactions to happen at lower temperatures and pressures than usually needed, saving money and energy
What factors affect the rate of a chemical reaction?
Concentration of reactants, temperature, surface area of solid reactants, and presence of catalysts
Why is increasing reaction rate economically important?
Higher reaction rates imply a higher rate of production, making processes more efficient and sustainable
How does surface area affect collision frequency?
Increasing surface area increases the number of exposed reactant particles, increasing collision frequency and reaction rate
What is the relationship between reaction time and rate of reaction?
Rate of reaction is inversely proportional to reaction time (1/time = rate of reaction)