Rate of Reaction Notes

Measuring the Rate of Reaction

• Rate of reaction can change over time.
• Rate of reaction can be measured by:
  • How much of a product is made in a given time.
  • How much of a reactant is used up in a given time.
• Collect gas using a syringe attached to a flask to measure the volume of gas produced at different times.

Anomalous Result

• An anomalous result is one that does not fit the pattern of the other results.
• To address an anomalous result:
  • Repeat the experiment to see if the result is still anomalous.
  • If the result is still anomalous, discard it.

Using Graphs

• Graphs show results from investigations into the rate of reaction.
• The slope/gradient of the line indicates how quickly the reaction is taking place.
• The steeper the slope, the faster the reaction.
• The line is steepest at the start of the reaction. As the slope decreases, the reaction slows down.
• When the line levels out, the reaction has ended.

Calculating Average Rate of Reaction

• Draw a line at the starting time on the horizontal axis up to the graph line (Point A).
• Draw a line at the ending time on the horizontal axis up to the graph line (Point B).
• Draw a line (C) between A and B; this represents the time taken.
• Line D shows how much product was produced in that time.
• Calculate the average rate of reaction by dividing the amount of product produced by the time taken.

Factors Affecting Rate of Reaction

• For a chemical reaction to occur, reactant particles must collide with enough energy.
• At the start:
  • Many unreacted particles are present.
  • Collisions happen frequently.
  • Product forms quickly.
• As the reaction progresses:
  • Fewer unreacted particles remain.
  • Collision chance decreases.
  • Product formation slows.
• Eventually, all particles react, collisions stop, and the reaction ends.

Surface Area and Rate of Reaction

• Only atoms/particles on the surface of a substance can react.
• Smaller pieces of solids react faster because they have a larger total surface area.
• Increasing the total surface area increases the rate of reaction.

Temperature and Rate of Reaction

• Increasing the temperature of reactants increases the rate of reaction.
• At higher temperatures, particles move faster, collide more often, and with more energy.
• The higher the temperature, the faster the rate of reaction.

Concentration and Rate of Reaction

• Increasing the concentration of reactants increases the rate of reaction.
• Higher concentration means more particles in a given space, leading to more frequent collisions.
• The higher the concentration, the faster the reaction.

Catalysts

• Catalysts speed up a reaction without being changed themselves.
• The same catalyst can be used repeatedly.
• Catalysts are often cheaper than increasing temperature, concentration, or surface area.
• Enzymes are biological catalysts.
• Catalase is an enzyme that speeds up the breakdown of hydrogen peroxide in living cells.
• Catalytic converters in cars use catalysts to reduce harmful gases.