topic 7

• What is the formula for rate of reaction?


  Rate of reaction = Amount of reactant used or amount of product formed / Time
• How can you investigate the rate of a precipiation reaction?

  Colour change will be from clear to cloudy

  Place the conical flask with the reaction in it on top of a white tile with a black cross drawn on it

  Time from the start of the reaction until the time that the cross is no longer visible - this is when the reaction is finished
• How can you investigate the rate of a reaction that gives of a gas? (2 things you can measure)

  volume of gas given off

  change in mass
• How can you find the change in mass in a reaction that gives off a gas?

  1) put cotton wool in the top of a conical flask where the reaction takes place

  2) make sure you record the starting mass, and start a timer

  3) take regular measurements of the mass and equal incriments of time

  4) when the mass stops changing (the conical flask should be on a mass balance), you know the reaction is finished and you should record the end mass

  5) calculate the change in mass against time
• Why do you need to put cotton wool in the top of a conical flask when investigating the change in mass in a reaction?

  (the reaction gives off a gas)


  because the cotton wool will mean the gas product can escape, but any liquid or solid reactants cannot
• How can you measure volume of gas given off during a reaction?

  - place a bung with a delivery tube connected to a gas syringe in the top of the conical flask where the reaction is taking place

  -after a set time interval measured with a stopclock, you can take the measurement of the volume of gas given off.
• What reactants would you use when measuring how surface area affects rate?

  -HCL acid

  - large marble chips, small marble chips, and chalk powder

  - the marble and chalk are both made from calcium carbonate
• How can you investigate how surface area affects rate?

  Use HCL and marble chips, use a gas syringe, measure volume produced at set time intervals

  repeat with smae conc and temp of HCL, but different sized marble chips/ powdered chalk
• Does powdered chalk or marble chips have a larger surface area?

  The powdered chalk
• How and why does surface area affect rate?

  The higher the surface area, the faster the rate because more particles are exposed so the greater the frequency of collisions.
• How and why does concentration affect rate?

  The higher the concentration, the higher the rate because the reactants are more crowded, which increases the frequency of collisions.
• How and why does temperature affect rate?

  The higher the temperature, the faster the rate, because:

  - The particles have more kinetic energy, which increases the frequency of collisions

  - more of the reactants have above the activation energy, so the collisions are also more likely to be successful as there is more energy in collisions
• How and why does the use of a catalyst affect rate?

  They increase the rate of reaction, and they do this by lowering the activation energy.
• What are biological catalysts called?

  enzymes
• Give an example of a biological catalyst used to produce beer?

  yeast
• How can you measure the affect of concentration on rate?

  1) place conical flask with HCL in on a mass balance

  2) add marble chips (set mass), and start stopclock (add cotton wool to neck of flask)

  3) record mass at set intervals, including 0 seconds

  4) repeat with different concentrations of HCL
• How can you investigate how temperature affects rate?

  1) measure out fixed volumes of sodium thiosulfate and HCL

  2) heat both to set temperature using a water bath

  3) add to conical flask on white tile with cross

  4) time until you can no longer see the cross when you look down the neck of the flask

  5) repeat with same (volumes of) reactants at different temperatures
• what happens to a catalyst after a reaction?

  it is chemically unchanged
• what is a catalyst?


  substance that speeds up the rate of a chemical reaction without being used up
• how do catalysts work?


  They lower a reaction's activation energy