Collison theory Flashcards
Kinetics is what
study of factors that affect the rates of chemical reactions
What is the collision theory
For a reaction to take place between two particles they must collide with enough energy to break bonds
The collision must take place must between the parts of the molecule that are going to react together so orientation plays apart.to get lots of collisions you need have a low volume.
so for fast rate lots of particles rapidly moving in small volume
why do collisions sometimes not lead to reaction
they didn’t collide with enough energy or in wrong orientation
Factors that affect rate of chemical reaction
temperature
concentration
catalyst
pressure of gas reaction
surface area of solid reactants
How does increasing temperature increase the rate of reaction
This increases the speed of the molecules, which in turn increases both their energy and the number of collisions
How does using a catalyst increase the rate of reaction
a catalyst is a substance which lowers the activation energy by finding an alternative reaction pathway
which means collisions can collide with less energy to react
How does increasing the concentration of a solution increase the rate of reaction
however what happens as the reaction proceeds
If there are more particles present in a given volume then collisions more likely and the reaction rate would be faster
However as a reaction proceeds , the reactants are used up and there concentration falls so in most reaction the rate of reaction drops as the reaction goes on
How does increasing the pressure of a gas reaction increase the rate of reaction
This is the same effect as increasing the concentration- there are more atoms/ molecules in a area of volume so collisions are more likely
How doe increasing the surface area of solid reactants
The greater the total surface area of a solid the, more particles that are available to collide with molecules in a gas or liquid
This means breaking a solid lump into smaller pieces increases the rate of reaction because there are more sites available
Only a very few collisions result in reactions
what is activation energy
For a collision to result in a reaction, the molecules must have a certain minimum energy, enough to start breaking bonds. The minimum energy to start a reaction
Transition state or activation complex what is it
species that exist at the top of the curve of an enthalpy diagram.
Some bonds are in the place of being made and some are in the place of being broken
like a ball at the very top of a hill it has extra energy and is unstable
What is a exothermic reaction
In an exothermic reaction, the reactants are higher in energy than the products
The reactants are therefore closer in energy to the transition state
This means that exothermic reactions have a lower activation energy compared to endothermic reactions
What is a endothermic reaction
Endothermic reaction
In an endothermic reaction, the reactants are lower in energy than the products
The reactants are therefore further away in energy to the transition state
This means that endothermic reactions have a higher activation energy compared to exothermic reactions
PRACTICE LOOKING AT THESE ENTHALPY GRPAHS AND LOOKING WHERE THE TRANSITION STATE WOULD BE ON EXOTHERMIC AND ENDOTHERMIC REACTION
NOT ALL FACTORS APPLY TO ALLL REACTIONS
