Lecture Notes: Graphs and Rates of Chemical Reactions

Objectives

• Draw and interpret graphs of the quantity of reactants or products in a chemical reaction.
• Calculate the mean rate of a chemical reaction.

Key Concepts

Graphs of Chemical Reactions

• Reactants to Products: In a chemical reaction, reactants turn into products.
• Graph Interpretation:
  • Plot the quantity of product formed against time.
  • Slope of the Line: Indicates the rate of reaction.
    • Steeper slope: Faster reaction.
    • Flat line (slope = 0): Reaction has stopped.
• Initial Reaction:
  • Fast due to a large number of reactant molecules.
  • Produces a lot of product in a short time.
• Slowing Reaction:
  • As reactants decrease, the formation of products slows.
  • Fewer reactant molecules are available.

Measuring Quantities

• Products: Measured in grams or centimeters cubed (for gases).
• Reactants: Can also plot the quantity of reactant used over time.

Mean Rate of Reaction

• Formula: Mean rate of reaction = Quantity of product formed / Time taken

Example Calculations

1. Example 1:

   • Given: 60 grams of product formed in 15 seconds.
   • Calculation: 60 g / 15 s = 4 grams per second.

2. Practice Problem 1:

   • Given: 20 grams of product formed in 40 seconds.
   • Solution: 20 g / 40 s = 0.5 grams per second.

3. Example 2:

   • Given: 30 grams of reactant used in 10 seconds.
   • Calculation: 30 g / 10 s = 3 grams per second.

4. Practice Problem 2:

   • Given: 150 grams of reactant used in 75 seconds.
   • Solution: 150 g / 75 s = 2 grams per second.

Resources

• Revision Workbook: Contains additional practice questions on rates of reaction.

Conclusion

• Ability to draw and interpret graphs for chemical reactions.
• Calculate mean rates of reactions effectively.