Kinetics (3.1.5) Flashcards
what is the activation energy?
the minimum energy needed for particles to collide successfully so a reaction occurs
what does collision theory state?
for reactant particles to react successfully, they must collide with sufficient energy and be in the correct orientation
why do most collisions not lead to a reaction?
the particles do not collide with sufficient energy (no successful collision)
what do Maxwell-Boltzmann curves show?
the distribution of molecular energies in gases at a constant temperature
what is true for molecules in a sample of a gas at a given temperature?
their average kinetic energy is constant
what are the key features of a Maxwell-Boltzmann distribution curve?
they start from the origin (no molecules with no energy)
curve is not bell-shaped (less steep on right side)
curve never meets x-axis (no maximum energy for molecules)
what are the different parts/explanations for a Maxwell-Boltzmann distribution curve?
a few particles have low energies because collisions cause some particles to slow down
the energy value for the peak is the most probably energy (Emp)
the mean energy of the particles is always a higher value than the most probable (higher value than the peak)
only a few particles have energy higher than the activation energy
the area under the curve represents the total number of particles present
what will the effect of increasing the temperature be on a Maxwell-Boltzmann distribution curve?
the total area under the curve will remain constant as number of particles in constant
at higher temperatures molecules will have a wider range of energies than at lower temperatures
the distribution of energies will shift to having more molecules with higher energies
the Emp and mean energies will shift to higher energy values (to the right), but the number of molecules with those energies decrease (peak will be lower down graph)
how can a reaction go to completion of few particles have energy higher than the activation energy?
particles can gain energy through collisions
what does rate of reaction mean?
the change in concentration of a substance in unit time, usually in mol dm^-3 s^-1
what is the qualitative effect of a change in temperature on the rate of a reaction?
as temp increases rate of reaction increases because the kinetic energy of particles increases so there is an increased frequency of successful collisions
how does Maxwell-Boltzmann distribution show the effect of temperature increase on rate?
the graph will show that a larger proportion of particles have energy higher than the activation energy (stays the same), so frequency of successful collisions increases
what is the qualitative effect of a change in concentration or pressure of a gas on collision frequency?
at higher concentrations or pressures there are more particles per unit volume so there is a greater frequency of successful collisions
how does Maxwell-Boltzmann distribution show the effect of concentration increase on rate?
the shape of the curve won’t change (Emp and mean energy remain same) but the curve for a higher conc will be higher and the area under it will be greater as there are more particles
this means more molecules have energy higher than activation energy
what is a catalyst?
a substance that increases the rate of a chemical reaction without being changed in chemical composition or amount
how do catalysts work?
by providing an alternative reaction route of lower activation energy
how does Maxwell-Boltzmann distribution show the effect of a catalyst on increasing rate of reaction?
the activation energy will be lower, so more particles will have energy higher than the activation energy, so there will be an increased frequency of successful collisions
what is the effect of a change in concentration on a reaction?
it will change the rate of the reaction and the amount of products
what is the effect of a change in volume on a reaction?
it will change the amount of product
what is the effect of a change in surface area on a reaction?
it will change the rate of the reaction
what is the effect of a change in temperature on a reaction?
it will change the rate of the reaction
