Rate of Reaction and Energy Changes in Chemical Reactions

• what must happen to the bonds in any chemical reaction?

  the bonds between atoms in the reactant molecules must break to allow the atoms to separate and rearrange to form new bonds to make the products.
• what causes covalent bonds between atoms to be broken in a chemical reaction?

  the reactant particles must be able to collide with sufficient kinetic energy for the covalent bonds between the atoms to break.
• what is activation energy?

  the minimum amount of energy needed for a reaction to occur,
• what does the activation energy for each chemical reaction depend on?

  the strength and number of bonds needing to be broken,
• what ability do reactions with a low activation energy have?

  they can occur spontaneously.
• what does combustion of a fuel need to occur?

  needs heat energy in the form of a lit match or flame to start the reaction.
• do most collisions that occur between reactant particles occur with energy equal to or greater than the activation energy?

  NO, most collisions wont be successful and no reaction will occur as the bonds between the atoms of the reactants aren't broken and the reactant molecules remain unchanged.
• providing that successful collisions occur, how does concentration of reactants and products change during a chemical reaction?

  concentration of reactants decreases and concentration of products increases.
• what is the equation for rate of reaction?

  rate of reaction = change in conc of products or reactants / time
• describe how concentration changes throughout a chemical reaction in detail.

  at the start of the reaction there are lots of reactant molecules around so the chance of success collisions occurring is higher. As the reaction proceeds the concentration of the reactants decreases as more are used up to make the products and the concentration of the products increases. As reactant molecules are used up the number of successful collisions occurring decreases and the change in concentration of reactants and products overtime decreases.
• what directly affects the rate of reaction>?

  the number of successful collisions.
• the higher the number of successful collisions occurring over a given time period..


  the higher the frequency of successful collisions and so the higher the rate of reaction will be,
• the lower the number of successful collisions occurring over a given time period..


  the lower the frequency of successful collisions and so the lower the rate of reaction will be.
• what are the units for concentration?

  moldm^-3
• what is concentration?


  a measurement of the number of moles of the substance present in 1dm3 of the solution.
• when one or both of the reactants is a solution, how can we change the concentration?

  either by changing the volume of the solution or the number of moles of substance present in the solution.
• what does a high concentration mean?

  there are a high number of moles present in the solution. The higher the number of particles present in the solution the higher the likelihood of successful collisions.
• what does an increase in the concentration of a solution result in?

  an increase in the number of successful collisions occurring over a given time period. So, the frequency of successful collisions increases resulting in an increase in the rate of reaction.
• what does a low concentration mean?

  there are fewer moles present in the solution, the lower the number of particles present in the solution the lower the likelihood of successful collisions.
• what does a decrease in the concentration of a solution result in?

  a decrease in the number of successful collisions occurring over a given time period. So, the frequency of successful collisions decreases resulting in a decrease in the rate of reaction.
• what is pressure?


  a measurement of the number of gas particles present in a specified volume of the gas.
• when one or both of the reactants is a gas, how can we change the pressure?

  by changing either the volume of the gas or the number of gas particles.
• what does a high pressure mean?

  there are a high number of gas particles present in the volume of gas, the higher the number of gas particles the higher the likelihood of successful collisions.
• what does an increase in the pressure of a gas result in?

  an increase in the number of successful collisions occurring over a given time period. So, the frequent of successful collisions increases resulting in an increase in the rate of reaction.
• what does a low pressure mean?

  there are fewer gas particles present, the lower the number of particles present the lower the likelihood of successful collisions.
• what does a decrease in the pressure of a gas result in?

  a decrease in the number of successful collisions occurring over a given time period. So, the frequency of successful collisions decreases resulting in a decrease in the rate of reaction.
• what are the particles like in a sample of gas?

  constant and random motion. Some particles move very fast and other move very slowly.
• what happens as gas particles move around?

  they collide with each other, during the collisions energy transfer occurs between the particles. Some particles gain energy and others will lose energy.
• what does a Maxwell-boltzmann distribution curve represent?

  the distribution of the energies of the particles in any sample of gas.
• look at this and learn.

  
• what does most probable energy mean?

  the amount of energy possessed by the majority of particles in the sample.
• what does mean energy mean?

  the average energy of the particles in the sample. This is always lower than the most probably energy.
• what does the area below the curve represent?

  the total number of particles in the sample of gas.
• in the Maxwell-boltzmann distribution curve, why are there no particles with 0 energy?

  all particles will have some energy.
• why should the Maxwell-boltzmann distribution curve never touch the x axis on the right hand side?

  there are always some particles present at the highest energues
• what can activation energy be shown by?

  Ea.
• what does any sample of gas contain?

  particles with a range of different kinetic energies.
• what makes a collision successful?

  if the particles have energy equal to or greater than the activation energy.
• does changes to the concentration of a solution or pressure of a gas change the energies of the particles?

  no, only the number of particles present is changed.
• how would the Maxwell-Boltzmann distribution Curve change if conc of solution or pressure of gas changes?

  the positions of the probable energy, mean energy and activation energy dont change. The curve would be drawn higher throughout to show there is an increased number of particles at each energy,