TOPIC 9 - KINETICS I

Question 1

understand, in terms of collision theory, the effect of a change in concentration on the rate of a chemical reaction

Answer 1

• increasing concentration speeds up reactions.
• there will be more particles in a given volume
• as the collision frequency is higher, the frequency of successful collisions is also higher so the rate of reaction is faster

Question 2

understand, in terms of collision theory, the effect of a change in surface area on the rate of a chemical reaction

Answer 2

• increasing surface area increase rate of reaction
• larger surface are means there are more exposed particles that can react

Question 3

understand, in terms of collision theory, the effect of a change in pressure on the rate of a chemical reaction

Answer 3

• increasing pressure increases rate of reaction
• there are more gas particles per unit volume
• frequency of collisions increases
• kinetic energy stays the same so there is the same proportion collisions but there are more collisions per second

Question 4

understand, in terms of collision theory, the effect of a change in temperature on the rate of a chemical reaction

Answer 4

• an increase in temperature causes an increase in rate of reaction.
• molecules have more kinetic energy at higher temperatures
• more particles have energy above the activation energy which results in an increase successful collision frequency

Question 5

what conditions do reactions need to take place

Answer 5

sufficient energy (activation energy)

Question 6

explain the Maxwell-Boltzmann distribution of molecular energies, how changes in temperature affect the rate of a reaction

Answer 6

• at low temperatures a smaller fraction of particles have at least activation energy
• at high temperatures a greater fraction of particles have at least activation energy
• catalyst shifts activation energy a little to the left so a higher proportion of particles have at least activation energy
• higher temperatures shift graph towards the right with a lower peak
• lower temperatures shift graph towards the left with a higher peak
• peak = energy that the highest fraction of molecules have

Question 7

what is the use of a solid (heterogeneous) catalyst for industrial reactions, in the gas phase

Answer 7

• heterogeneous catalyst is a catalyst that is in a different phase from the reactants i.e. in Haber process, gases are passed over a solid iron catalyst
• the reaction happens on the surface of the catalyst
• increasing the surface area of the catalyst increases the number of molecules that can react at the same, increasing the rate of the reaction.
• the catalyst lowers activation energy by providing an alternative pathway

Question 8

what are the economic benefits of the use of catalysts in industrial reactions

Answer 8

• lower productions costs
• form more products in a shorter time
• use milder conditions so less energy and money are used
• speed up reactions