02 - rate equations

• what does the relationship between concentration and rate reveal?

  an increase in concentration of reactants causes rate of reaction to increase. Because when concentration increases there are more particles in the same volume which have energy equal to or greater than activation energy. So, more successful collisions occur over a given time and the rate of reaction increases.
• is the relationship between concentration and rate of reaction proportional?

  not always, eg: in some reactions doubling the reactant concentration can double the rate of reaction. But, in other reactions doubling the concentration may cause rate to quadruple. Some changes in concentration don't have any effect on rate of reaction.
• what is the equation for the rate equation?

  rate = k[A]^m[B]^n

  m and n = the orders of reaction

  A and B = reactants

  k = rate constant.
• what is the order of reaction?

  the power to which the reactant concentration is raised in the rate equation.
• what is the rate constant (k)?

  the constant of proportionality which relates the concentration of the reactants to the rate of reaction.
• how is the order of reaction determined? what can this provide?

  experimentally and can provide info about the mechanism of the reaction.
• for an investigation looking at the effects of concentration changes on reaction rate, why must the temperature be kept constant?

  so the temperature doesn't affect the energies of particles and so the rate of reaction.
• the rate constant is constant as long as...


  ...the temperature is kept constant.
• what can we assume about investigations involving changes to concentration regarding the value of rate constant?

  we can calculate the value of rate constant (k) for any experiment and it would be exactly the same through the whole investigation.
• what must be kept constant when investigating the effect of temperature changes on rate of reaction?

  the concentrations of the reactants.
• what is rate of reaction dependent on?

  the value of k
• what does the value of k vary because of?

  different temperatures.
• what does the Arrhenius equation explain?

  why the value of k varies with temperature
• what is the expression for 'the number of particles in a sample with energy equal to or greater than activation energy'?

  e^-Ea/RT
• what is the equation for rate constant (k)?

  k = Ae^-Ea/RT

  k = rate constant

  Ea = activation energy

  R = 8.31

  t = temp (k)

  A = the Arrhenius constant

  e = maths function (2.711828)
• open our calculator, how do we use e?

  we don't need to know e's value, we use the In button and press shift.
• what is the equation to calculate activation energy by rearranging Arrhenius equation?

  Ink = -Ea / RT + InA
• how to go from Jmol^-1 to KJmol^-1?

  divide by 1000
• what is the rate of a chemical reaction defined as?

  a change in a measured property over a specific time period. eg: change in mass of reactants, volume of gaseous products formed, change in colour of solution as reactants used or products formed.
• what dictates which practical method of measurement chosen?

  the type of reaction occurring and the states of the reactants and products.
• what is required practical 7?

  measure the rate of chemical reactions using a continuous monitoring method and an initial rate method.
• what is a continuous monitoring method?

  any method involving taking measurements at specific time intervals during the reactions.
• what are some examples of continuous monitoring methods?

  colorimetry, mass change, titration and volume of gas evolved.
• when is colorimetry used?

  if one of the reactants or products is a coloured solution.
• how does colorimetry work?

  measures the intensity in the colour of a solution. The colorimeter uses a light source to shine white light through a filter into the reaction mixture. Some frequencies of the white light are absorbed by the sample and others are transmitted through the sample. The progress of the reaction is followed by monitoring the changes in colour intensity of the solution over time during the formation of a coloured product or removal of a coloured reactant.