6..., 16... Flashcards
Rate fo reaction
rate of reaction at a particular time is the gradient of the curve (conc vs time graph)
rate = change in conc/change in time
methods of measuring rates of reaction
Volume of gas produces
change in mass
change in color
change in concentration by titration
Factors that affect rate of reaction
- concentration
- pressure
- temperature
- surface area
How does concentration effect rate of reaction
As the concentration increases, the rate of reaction increases
- at higher concentration the collision between particles is more frequent
how does pressue affect the rate of reaction
as pressure increases, the rate of reaction increases
- there are more particles in a given volume (conc inc.), increasing the frequency of collisions
how does temperature effect the rate of reaction
as temperature increases, the rate of reaction increases:
- kinetic energy of particles increases so collisions are more frequent
- a greater proportion of reactant particles have enough energy
how does surface area effect the rate of reaction
As surface area increases (particle size decreases), the rate of reaction increases:
* Collisions are more frequent.
Collision Theory
Collision theory – in order for a chemical reaction to occur, two or more reactant particles must collide.
- particles must collide with thte correct orientation
- particles must collide with sufficient energy
Activation energy
Activation energy is the minimum amount of kinetic energy that particles must have for a chemical reaction to occur.
Maxwell - Boltsmann Distribution
The area under the curve is equal to the total number of particles in the sample.
- Only the area under the curve past Ea represents the number of particles that
- have enough kinetic energy to react (activation energy).
y-axis: probability distirbution/# of particles, x-axis: kinetic energy
What happend to the Maxwell-Boltzmann Distribution graph change when temperature increases
- The maximum of the curve shifts right.
- The curve flattens (total area under the curve remains constant).
- There is an increase in area under the curve to the right of E (at higher temperatures, a greater proportion of particles have kinetic energy equal or greater than the activation energy).
Kinetic theory
Absolute temperature (Kelvin) is directly proportional to the average kinetic energy of gas particles.
Absolute zero (0K) is the lowest possible temperature on the Kelvin scale.
* In a Maxwell-Boltzman curve, it is the origin of the x-axis.
* The motion of particles in minimal.
* A substance has no transferable heat energy.
* An ideal gas at constant pressure would reach zero volume.
Catalysts
increase the rate of reaction while remaining chemically unchanged. They
provide an alternative reaction pathway with a lower Ea.
By lowering the Ea, a greater proportion of reactant particles have sufficient energy to react.
rate equation
Where m and n are the orders with respect to their reactants
Order of reaction = m + n
Molecularity
the number of molecules or atoms involved as reactants in the elementary reaction
Unimolecular: Single molecule or atoms involved in an elementary step
Bimolecular: Two molecules or atoms involved in an elementary step
Zero order graphs
First order graphs
second order graphs
Arrhenius Equation
uses temperature dependece of the rate constant to determin activation energy
A: frequency factor, takes into account the frequency of collisions with proper orientations
graph of lnk against 1/T is a linear plot with a gradient of -Ea/R and intercept lnA
rate constant
- replacing the values in the rearranged rate equation with the units of that value
- The units can then be combined or cancelled as required
