Chapter 9- Rates Of Reaction Flashcards
Definitions, formulae and key ideas
Definition of rate of reaction plus the unit
A measure of the rate at which reactants are used up or the rate at which products are formed .
Unit : moldm^-3s^-1 or moldm^-3/s
Definition of activation energy
The minimum energy that colliding particles must possess for a successful collision that results in a reaction to take place.
Definition of a catalyst
A substance that increases the rate if reaction but remains chemically unchanged itself at the end of the reaction.
Definition of Boltzmann distribution
A graph showing the distribution of energies of the particles in a sample at a given temperature.
Definition of substrate
A molecule that fits into the active site of an enzyme and reacts
State the collision theory :
In order to react with each other , particles must collide in the correct orientation and with sufficient energy (a successful collision ). The particles might be atoms, ions, or molecules.
Describe an unsuccessful collision
When reactant products collide and bounce off without changing. This will take place if colliding particles do not have enough energy to react.
According to the collision theory, a reaction will speed up if 2 things happen , namely:
And a sentence stating both of these in it simply
- The frequency of collisions increases
- The proportion of particles with energy greater than the activation energy increases
Therefore, the rate of reaction will increase if the number of successful collisions per unit time increase.
The more concentrated a solution , means
The greater number of particles of solute dissolved in a given volume of solvent.
Explain the effect of increased concentration on reaction rate …
Faster rate of reaction because the random motion of particles in solution results in more frequent collisions between reacting particles .
More frequent successful collisions per unit time.
What is the effect of increasing the pressure of reacting gases on the rate of reaction ?
This means that there are more gas molecules in a given volume. This results in more collisions per unit time , and a faster reaction.
What happens if you raise the temperature of a reaction mixture , to the rate of reaction? 3 points
The average kinetic energy of particles increases. The particles therefore move faster and with more energy , resulting in more frequent collisions and so the proportion of successful collisions per unit time, increases.
Page 144 boltzmann distribution and the effect of increase in temp.
Flattens and peak shifts to the right .
Greater proportion of molecules exceed the activation energy
How do catalyst works ?
The provide an alternative reaction pathway (mechanism) with a lower activation energy
How does a catalyst affect the boltzmann distribution ?
The shape stays the same but there is a new line added called Ea (cat) that comes before the normal Ea
Describe a homogeneous catalyst
When a catalyst and the reactants in a catalysed reaction are in the same phase.
Describe a heterogeneous catalyst
A catalyst in a different phase to the reactants in a catalysed reaction.
Many heterogeneous catalysts are solids that catalyse gaseous reactants . The reactions take place on …
The surface of the solid catalyst.
Enzymes are what ?
Biological catalyst
Explain what catalyst do in living things ?
They are large protein molecules which enable the biochemical reactions that happen in living things to take place very quickly at relatively low temperature.
Enzymes catalysis have 5 specific features ?
Not NB to know
- Enzymes are more efficient than inorganic catalysts
- Enzymes are specific, they usually only catalyse one particular reaction
- As a consequence of this specificity , enzymes do NOT produce byproducts
- Enzymes work under very mild conditions, otherwise they get denatured
- The amount of enzyme present in a cell can be regulated
