Topic 1- Rates Flashcards
How can reaction rate be calculated?
Change/time interval
1/time (relative rate)
What are rates of reactions affected by? (5)
Concentration Pressure Particle size Temperature Catalysts
What is the collision theory?
States that reactants must collide with the correct geometry and possess a min energy(activation energy) before a successful reaction occurs
What is temperature?
A measure of the av kinetic energy of the particles of a substance
What is the activation energy?
Is the min kinetic energy required by colliding particles before reaction will occur
What are energy distribution diagrams used for?
To explain the effect of changing temp on the kinetic energy of particles
Why does increasing the concentration increases the rate?
Increases the number of particles in a given vol which means there are more successful collisions
Why does increasing the pressure of a gas increase the rate?
Increases the conc of the gas which increase the no of particles in a given volume which means there are more successful collisions
Why does decreasing the particle size increase the rate?
Increases the surface area of the reactant, this increases the no of possible collisions, therefore the rate of successful collisions will increase
Why does an increase in temperature increase the rate?
Because the av kinetic energy of the colliding particles increases, thus means that more particles collide with the Ea resulting in more successful collisions
What is a catalyst?
They increase the rate of a reaction by providing an alternative reaction pathway with a low activation energy
What is the activated complex?
A high energy unstable arrangement of atoms it is formed at the top of the activation energy barrier
Why do reaction rates have to be controlled? (2)
If they are too low=not economically viable
If they are too high= risk of thermal explosion
What do negative catalysts do?
They decrease the rate by increasing the activation energy
What is a heterogeneous catalyst? Give example
They exist in different state to reactants. They are solids that catalyses reactions between reactants that are gases, liquids or in solution. e.g. which catalyses the reaction between hydrogen and nitrogen in the Haber process.
What is a homogeneous catalyst? Give example
They exist in the same state to reactants. E.g. Enzymes are homogeneous catalysts as they are found in aqueous solution and the reactants are also in aqueous.
What effect does a catalyst have on enthalpy change?
no affect
How do you calculate the overall enthalpy change of a reaction?
Energy of the products - Energy of the reactants
Ep-Er
When new bonds are formed, is that an exothermic or endothermic reaction?
Exo
What are the 3 steps of catalysis occurring on the active sites of heterogeneous catalysts?
Step 1- adsorption ( molecules of one or both reactants form both with the catalyst, the weakens the bonds with molecules)
Step 2- Reaction (the molecules react on the catalyst surface.)
Step 3- Desorption (the product molecules leave the catalyst and the vacant site can be used again)
What is an active site?
The points on the surface of the solid catalyst were the reactant molecules become absorbed
How do you increase the number of active sites?
A thin layer of the catalyst is often coated onto beads to increase the surface area upon which the reaction can take place.
