Reaction rate definition
change in concentration (or amount) of a reactant or product over time
Reaction rate equation
Rate of reaction=amount of reactant used up or product formed/time
Collision theory
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
Factors affecting rate of reaction
- 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
Maxwell-Boltzmann distribution curve
- 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
Factors affecting the Maxwell-Boltzmann distribution curve
- 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
Types of catalysts
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
How do changes in temp affect the Maxwell-Boltzmann distribution curve?
- 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
How does a catalyst affect the Maxwell-Boltzmann distribution curve?
- catalyst lowers Ea=up proportion of molecules with energy > Ea=up frequency of successful collisions=up rate of reaction
