pmt

• What is the equation for rate of reaction?

  rate of reaction = amount of reactant used or product formed/ time (s)
• what units could be used for rate of reaction?

  • g/s
  • cm$^3$/s
  • mol/s
• how can you measure the rate of reaction when a gas is give off?

  • measure time + collect gas in an upside down measuring cylinder in a trough of water
  • or in a gas syringe to measure the volume of gas produced
  • measure time and change in mass
• How can you measure the rate of reaction when a precipitate is formed?

  • put a black cross below a beaker containing one reactant
  • time how long it takes for cross to disappear after second reactant = added
• Why is using the precipitation method to investigate rate of a reaction not very accurate?

  • it = subjective: people = likely to disagree over exact point at which cross is no longer visible
• How can you measure rate of reaction using a digital balance?

  • when a gas = produced as this will cause mass to decrease
  • the experiment can be carried out on a digital balance + rate of reaction can be calculated by recording mass at regular time intervals
• What does the term 'activation energy' mean?

  • minimum amount of energy required for a reaction to occur between two reacting particles
• What must happen for a reaction to occur?

  • particles must collide at the correct orientation
  • with sufficient energy to react
• in terms of particles, what 2 things could happen when the rate of reaction increases?

  • more frequent collisions
  • energy of collisions increases
• how can rate of a reaction be increased?

  • increase temperature
  • increase concentration
  • increase surface area to volume ratio
  • add a catalyst
  • increase the pressure (for gases)
• how does temperature affect the rate of reaction?

  • increasing temperature increases the rate of reaction
  • because reactants have more energy
  • so more particles have energy above activation energy: means more collisions will be successful
  • collisions also occur more frequently because particles have more kinetic energy
• how does surface area affect the rate of reaction?

  • increasing surface area of reactants increases the rate of reaction
  • because a greater surface area means there are more exposed particles so more frequent successful collisions
• how does a catalyst affect the rate of reaction?

  • catalyst increases the rate of reaction
  • because provides an alternate reaction pathway
  • with a lower activation energy
  • more particles will have sufficient energy to overcome the activation energy + react so more successful collisions occur at the same time
• how does concentration affect the rate of reaction?

  • increasing concentration increases the rate of reaction
  • because there are more reacting particle in the same volume
  • so there are more frequent successful collisions
• How does pressure affect the rate of a gaseous reaction?

  • increasing pressure of a gaseous reaction increases the rate of reaction
  • because there are more reacting particles in the same volume of gas (or same number of particles in a smaller volume)
  • so more frequent successful collisions occur
• marble chips react with hydrochloric acid to produce calcium chloride, water and carbon dioxide. How could you measure the rate of reaction?

  • gaseous carbon dioxide is released
  • the rate can be measured by using a digital balance to measure the change in mass over a period of time
• marble chips react with hydrochloric acid to produce calcium chloride, water and carbon dioxide. How could the rate of this reaction be increased?

  • increase the surface area of the marble chips by turning them into a powder.
  • increase concentration of acid
  • increase temperature
• after completing an experiment, how can you find the rate of reaction using a graph?

  Plot:

  • X axis: time
  • Y axis: amount of reactant used or product formed

  draw a tangent to a point on the graph + find the gradient of this line to find the rate of reaction at that time
• what does a graph that shows the amount of gas given off with a steep gradient tell you about the rate of reaction?

  • a fast rate of reaction
• a graph is plotted to show time and the amount of gas given off during a reaction. Describe the shape of the curve

  • initially: curve is very steep as rate of reaction is relatively fast at the start
  • curve becomes less steep as reactants get used up because there are fewer successful collisions occurring
  • end: graph is a flat line because all the reactants have been turned into products
• what is a catalyst?

  • substance that speeds up the rate of a reaction without being chemically changed at the end
• how does a catalyst speed up the rate of a reaction?

  • provides an alternate reaction pathway with a lower activation energy
• what are enzymes?

  • biological catalysts that increase the rate of reactions in living cells
• which enzyme is used to produce ethanol from glucose?

  yeast
• what do the terms exothermic and endothermic mean?

  • endothermic: reaction that takes in heat energy from the surroundings
  • exothermic: reaction that gives out energy to the surroundings
• are neutralisation reactions endothermic or exothermic?


  exothermic
• are displacement reactions endothermic or exothermic?

  • either exothermic or endothermic
• is a salt dissolving in water endothermic or exothermic?

  • either exothermic or endothermic
• are precipitation reactions endothermic or exothermic?


  exothermic
• how could you measure the temperature change of a neutralisation reaction?

  1. measure initial temperature of the solutions
  2. mix both reactants in a polystyrene cup
  3. record highest temperature reached
  4. calculate temperature change
• when measuring the temperature change of a reaction, heat loss means that measurements may be inaccurate. how could heat loss be minimised during an experiment?

  • use polystyrene cup
  • place reaction cup in a beaker full with cotton wool for extra insulation
  • lid on the reaction cup
• Describe exothermic and endothermic reactions in terms of bonds breaking/forming, what happens during a chemical reaction?

  • energy is needed to break bonds + released when bonds are made
  • exothermic: energy released from breaking bonds = greater than energy used to make bonds
  • endothermic: energy released in forming new bonds = greater than energy used to break old bonds
• what two types of reaction are exothermic?

  • combustion
  • neutralisation
• give an example of an endothermic reaction

  • thermal decomposition
  • photosynthesis
• how can the energy change of a reaction be calculated from bond energies?

  energy change (kJ mol$^{-1}$) = total energy of bonds broken - total energy of bonds made
• if the energy change of a reaction is negative, is the reaction exothermic or endothermic?

  • exothermic
  • energy has been lost to the surroundings
• what is a reaction profile?

  • graph showing relative energies of reactants and products
  • as well as the activation energy of a reaction