Rate of Reaction

• What is the rate of a chemical reaction?

  Change in concentration of reactants or products per unit time.
• How can you measure the quantity of a reactant or product?

  In g, cm³ or mol.
• What are the possible units for rate of reaction in GCSE?

  g/s or cm³/s or mol/s
• Where on a rate graph is the end of the reaction? 


  The time at which the amount is no longer increasing or decreasing.
• How can you sketch a rate graph showing a faster rate?

  Pick a point to the left of the end of the reaction and draw a curve up to it.
• How can you sketch a rate graph showing a slower rate?

  Pick a point to the right of the end of the reaction and draw a curve up to it.
• How can you work out rate from a point on a graph?

  Draw a tangent to the curve at the point and calculate the gradient.
• How can you work out mean rate between two points from a graph?

  Draw a straight line between the two points and calculate the gradient.
• How can you work out mean rate between two points from a graph?

  Draw a straight line between the two points and calculate the gradient.
• What is the first thing to do when writing a rate experiment plan?

  Add the two measured amounts of reactants together
• What is the second thing to do when writing a rate experiment plan?

  Describe the change being timed with a timer and that the time taken must be recorded.
• What is the final thing to do when writing a rate experiment plan?

  Repeat the experiment and change the independent variable.
• IV

  what is changed
• DV

  what is measured
• How can an experiment be made valid?

  By taking repeat readings and controlling variables.
• How can validity be improved?

  By taking more repeat readings, a greater range of readings and controlling more variables.
• What variables might be controlled in a rate experiment?

  Initial temperature, volume or concentration of solution, mass of solid.
• How are curve patterns on line of best fit described?

  As an increasing or decreasing rate increase or decrease.
• What factors can affect the rate of a reaction?

  Temperature, surface area, concentration, pressure.
• Explain why increasing the surface area increases the rate of a reaction.

  Surface area to volume increases so the frequency of collisions increases.
• Explain why increasing the concentration increases the rate of reaction.

  There are more particles per unit volume and frequency of collisions increases.
• Explain why increasing the pressure of a gas increases the rate of a reaction.

  There are more particles per unit volume and frequency of collisions increases.
• Explain why increasing the temperature increases the rate of reaction.

  Particles move faster and many more particles have energy greater than the activation energy, frequency of collisions increases.
• Explain why rate doubles when concentration doubles.

  Doubles the number of particles per unit volume and frequency of collisions doubles.
• Explain why all chemical reactions slow down and eventually stop.

  Their concentration decreases as reactants get used up. Number of particles per unit volume decreases so frequency of collisions decreases until all reactants are gone.
• What is a catalyst? 


  Something which changes the rate of a reaction but is not used up in that reaction.
• How do catalysts speed up reactions?

  They provide an alternative reaction pathway that has a lower activation energy.
• Are catalysts included in reaction equations? 


  No
• What are the benefits of catalysts? 


  They allow reactions to run at lower temperatures which saves energy.
• What is a biological catalyst called? 


  An enzyme.