FC24: Rates of Reactions Flashcards
Describe the collision theory
In order for a reaction to occur, reactant particles must collide with sufficient energy, collisions that exceed the activation energy are successful collisions, the more frequent the collisions, the more likely successful collisions occur in a given time
List 4 factors that increase the frequency of collisions
increase in temperature
increase in pressure of gases
increase in concentration of solutions
increase in surface area of solids
How do catalysts affect collisions
do not increase frequency or energy of collisions, but lowers activation energy and so frequency of successful collisions increases in a given time
What is a Boltzmann distribution curve
a model to explain the effect of temperature and/or a catalyst on the rate of reatcion of gases
What is the x-axis and y-axis title of a Boltzmann distribution curve
x-axis = kinetic energy
y-axis = number of particles with KE
What are two things to make sure you do when drawing a Boltzmann distribution curve and why
1 - line always touches origin (as there are no particles therefore no energy)
2 - line never touches x-axis after origin ( as there are always particles with very high energy)
what does the total area under a Boltzmann distribution curve represent
the total number of particles
what does the area under a Boltzmann distribution curve and above the activation energy represent
the total number of particles that exceed the activation energy and therefore can react
What does a catalyst do to rate of reaction (using collision theory and Boltzmann distribution curve)
Adding a catalyst lowers the activation energy by providing an alternative reaction pathway, this increases the area under the curve and above the Ea, therefore a greater proportion of particles exceed the Ea per unit time, therefore increasing the frequency of successful collisions and so increasing the rate of reaction
What does an increase in temperature do to rate of reaction (using collision theory and Boltzmann distribution curve)
Increasing the temperature increases the area under the curve and above the Ea, therefore a greater proportion of particles exceed the Ea per unit time, therefore increasing the frequency of successful collisions and so increasing the rate of reaction
What does an increase in temperature do to a Boltzmann distribution curve
shift to the right
peak is lower but end of curve is higher than original curve
What does an decrease in temperature do to rate of reaction (using collision theory and Boltzmann distribution curve)
Decreasing the temperature decreases the area under the curve and above the Ea, therefore a smaller proportion of particles exceed the Ea per unit time, therefore decreasing the frequency of successful collisions and so decreasing the rate of reaction
What does an decrease in temperature do to a Boltzmann distribution curve
shift to the left
peak is higher but end of curve is lower than original curve
What are homogenous catalysts
where the catalyst is in the same phase as the reactants (solid, liquid, gas)
What are heterogenous catalysts
where the catalyst is in a different phase to the reactants (solid, liquid, gas)
