Chapter 7: How far? How fast? Flashcards
Define chemical bonds:
Forces of attraction between atoms or ions
Define endothermic process:
a process that breaks bonds and takes heat in.
Negative heat of reaction.
Define exothermic process:
a process that makes bonds and gives heat out.
positive heat of reaction.
Define heat of reaction:
the energy change going from reactants to products in a chemical reaction.
Define bond energy:
the average value obtained for a particular bond.
What is an energy level diagram?
a representation of what happens during a reaction in terms of energy.
How do you calculate bond energies?
energy to break bond - energy to form bond
Define activation energy:
the minimum kinetic energy that particles must have before a reaction can happen. (energy needed to break old bonds before new ones can be formed)
define the rate of a chemical reaction:
the time taken for a specific quantity of reactant to be used up or for the product to be formed.
How do you calculate the rate of reaction?
change in quantity of products/ time taken for the change
also calculated from the tangent of a graph
How to calculate the mean rate of reaction?
quantity of product formed/ time taken
Factors that affect rate of reaction:
- temperature
- concentration
- surface area of reactant
- presence of catalyst
Define catalyst:
a substance that increases the rate of a chemical reaction and remains chemically unchanged at the end of the reaction.
provides an alternative pathway for a reaction.
What is a photochemical reaction?
a reaction that is activated by the absorption of light which transfers energy to the reactants that then react.
define a reversible reaction:
a reaction that can be reversed if we change the conditions that the reactions are in.
define a forward reaction:
represented by a chemical equation and by convection the reaction goes from left to right.
define chemical equilibrium:
when in an enclosed system both the forward and backward reactions are equal and therefore the products formed are used up as soon as they are made.
State Le Chatelier’s principle:
when a system’s conditions change the system will do something opposite to try and come back to equilibrium. ( the equilibrium therefore shifts )
Conditions of the Haber process:
- N2 and H2 are mixed in the ration 1:3
- optimum temperature (450) and pressure (200 atmospheres) is applied
- a catalyst of finely divided iron is used
- ammonia is condensed out and H2 + N2 are reused
State the collision theory:
a chemical reaction can only take place when the reacting particles collide with each other and have sufficient energy.
