Kinetics

Question 1

Reaction rate definition

Answer 1

change in concentration (or amount) of a reactant or product over time

Question 2

Reaction rate equation

Answer 2

Rate of reaction=amount of reactant used up or product formed/time

Question 3

Collision theory

Answer 3

Orientation - The particles must collide in the correct orientation. They need to be facing each other appropriately.
Energy - The colliding particles need at least a minimum amount of kinetic energy ie Ea
- most collisions are non-effective because they fail to satisfy one or both conditions=x reaction
- reactions with low Ea=occur more easily

Question 4

Factors affecting rate of reaction

Answer 4

• SA=more SA exposed=more particles available to collide=more frequent successful collisions
• conc=high conc=more particles per unit volume=particles closer tgt=more frequent collisions
• pressure=high pressure forces gas particles closer tgt=more particle per unit volume=more frequent collisions
• temp=high temp=more Ek of particles=move faster=more frequent collisions+more particles will meet Ea=higher proportion of successful collisions
• catalyst=provides alternative pathway w a lower Ea=particle require less energy to react=more particles have Ea

Question 5

Maxwell-Boltzmann distribution curve

Answer 5

• The curve starts at the origin=no molecules have zero kinetic energy
• the total area under the curve=total number of molecules.
• peak of the curve shows the most probable kinetic energy a molecule can have

Question 6

Factors affecting the Maxwell-Boltzmann distribution curve

Answer 6

• area under graph remains constant
• increasing temp=curve gets broader+flatter due to greater spreads+shift to higher energies/velocities=more molecules with Ea
• decreasing temp=curve gets narrower+pointy due to smaller spreads+shift to lower energies/velocities=less molecules have Ea
• adding a catalyst=lowers Ea=shifts to the left=more molecules with Ea=greater area under curve

Question 7

Types of catalysts

Answer 7

homogeneous=catalyst is in the same phase as reactants eg all in solution
heterogeneous= catalyst is in a diff phase to reactants eg catalyst is solid+reactants gases

Question 8

How do changes in temp affect the Maxwell-Boltzmann distribution curve?

Answer 8

• higher temp=MB distribution curve flattens (=total no molecules is constant+area under curve is the same=lower peak height) and the peak shifts to the right (=more molecules reached Ea)=higher proportion of molecules w energy > Ea
• shift=both frequency of collisions
  +proportion of successful collisions increase with temp=even a small rise in temp can lead to a significant increase in the rate of reaction.
• higher temp=up mean energy of molecules=wider spread of values

Question 9

How does a catalyst affect the Maxwell-Boltzmann distribution curve?

Answer 9

• catalyst lowers Ea=up proportion of molecules with energy > Ea=up frequency of successful collisions=up rate of reaction