Kinetics Flashcards
when do successful collisions take place
For a reaction to occur
successfully, these collisions must have energy greater than or equal to the activation
energy of the reaction and the particle orientation must be correct
when do chemical reactions take place
Chemical reactions occur when particles of substances collide.
Reaction Conditions
The conditions of a reaction impact the collisions of the particles and can be altered to provide
the particles with more energy. Therefore the conditions can be changed to increase the
likelihood of a collision occurring with sufficient energy to react in order to increase rate.
how to calculate rates of reaction
Rate of reaction can be calculated from empirical data that has been plotted on graphs.
how to calculate rates of reaction On a concentration-time graph,
On a concentration-time graph, the rate of reaction is equal to the gradient of the curve at a
given point. Therefore the graph can be used to find the rate by drawing a tangent to the curve
at a given time.
Maxwell-Boltzmann Distribution
Not all molecules in a substance have the same amount of energy. Their energies are
distributed in a pattern called the Maxwell-Boltzmann
zero
zero particles have 0 energy
most probable
most common energy
does Changing the reaction conditions alter the shape of the curve
Changing the reaction conditions will alter the shape of the curve so that the number of
particles with energy greater than the activation energy is different.
total area under the curve
The total area under the
curve represents the total number of molecules in the sample, therefore it must remain
constant.
Effect of Temperature
thermal energy is transferred to it. This energy is converted to kinetic energy and the molecules of the substance move faster and further.
Increased
movement of the molecules means collisions would occur more often and with greater
energy.
As a result, of increased Temperature
As a result, more collisions have energy greater than the activation energy and result in
a reaction.
Therefore increasing the reaction temperature will increase the rate of reaction as more
collisions of greater energy occur in a given time.
The Maxwell-Boltzmann distribution at an increased temperature shifts to the
right so that a greater proportion of molecules have energy greater than or equal to the activation energy.
Effect of concentration Pressure
When the concentration of a sample is increased, more molecules of substance occur in the
same volume meaning they are packed closer together. Therefore collisions between
molecules become more likely and the chances of a collision occurring with energy greater
than the activation energy increases. As a result, the rate of reaction increases.
.
Effect of Pressure
Increasing pressure has a similar effect as molecules are packed closer together into a
smaller volume
concentration and pressure increased effects on the maxwell boltzmann
The Maxwell-Boltzmann distribution is shifted to the right.
Effect of Catalysts
A catalyst is a substance that increases the rate of reaction without being used up in the
reaction. It works by providing an alternative reaction path that requires a lower activation
energy for the reaction to occur.
Effect of Catalysts maxwell boltzmann
The Maxwell-Boltzmann distribution curve is unchanged in shape but the position of the
activation energy is shifted to the left so that a greater proportion of molecules have sufficient
energy to react.
Heterogeneous Catalysts
These are catalysts that are in a different phase or state to the species in the reaction.
Heterogeneous Catalysts example
An
example of this is the Haber Process, where a solid iron catalyst is used to speed up the
reaction between hydrogen and nitrogen gases.
Transition metals make good catalysts due to their variable oxidation states.
how does Heterogeneous Catalysts work
Electrons are
transferred to produce a reactive intermediate and speed up the reaction rate. An example of
this is the Contact Process which uses a vanadium oxide catalyst to speed up the conversion
of sulfur dioxide to sulfur trioxide.
Measuring reaction rates calculation
amount of reactant used or product formed/ time
measuring the rates of reaction examples
time it takes to form a precipitate
change in mass
gas volume
time it takes to form a precipitate
sodium thiosulfate and colorless hydrochloric acid
change in mass
hydrochloric acid and calcium carbonate
gas volume
magnesium and any acid
