Chemistry Paper 2 Topic 6 Flashcards
Topic 6: The rate and extent of chemical change.
What is the rate of a chemical reaction?
The rate of a chemical reaction is how fast the REACTANTS are CHANGED into PRODUCTS.
Give an example of a SLOW chemical reaction.
Rusting of Iron, Chemical weathering ( Acid Rain )
Give an example of a MODERATE chemical reaction.
Magnesium reacting in ACID to produce a gentle stream of bubbles.
Give an example of a FAST chemical reaction.
Explosions; release LOTS OF GAS and Explosion reactions are all over in a fraction of a second.
On a rate of reaction graph, how is a FAST reaction represented?
The quickest reactions have the STEEPEST lines and become FLAT in the LEAST TIME.
What do FLAT lines represent on rate of reaction graphs?
FLAT lines show the reaction has FINISHED.
In terms of COLLISION THEORY; explain how COLLISION FREQUENCY affects the rate of reaction.
The COLLISION FREQUENCY of reacting particles (how often they collide). The MORE collisions there are the faster the reaction is. E.g. doubling the frequency of collisions doubles the rate.
What else does the RATE of chemical reactions depend on?
The RATE of chemical reactions also depends on the energy TRANSFERRED during a collision. Particles have to collide with ENOUGH ENERGY for the collision to be SUCCESSFUL.
What is the MINIMUM AMOUNT of energy that particles need to react called?
The MINIMUM AMOUNT of energy that particles need to react is called ACTIVATION ENERGY. Particles need this energy to BREAK THE BONDS in the reactants and start the reaction.
What is ACTIVATION ENERGY?
ACTIVATION ENERGY is the MINIMUM AMOUNT of energy that particles need to react
What are the FOUR things Rate of Reactions DEPEND on?
- TEMPERATURE.
- The CONCENTRATION of a solution or the PRESSURE of gas.
- SURFACE AREA - this changes depending on the size of the lumps of a solid.
- The presence of a CATALYST.
Why does INCREASING the TEMPERATURE affect the rate of reaction?
When the TEMPERATURE is INCREASED, the particles all move FASTER; INCREASING the FREQUENCY of COLLISION. (the particles are going to collide more)
Also, the faster they move the MORE ENERGY they have, so MORE of the COLLISIONS will have ENOUGH ENERGY to make the reaction happen.
Why does INCREASING the CONCENTRATION or PRESSURE affect the rate of reaction?
If a solution is made MORE CONCENTRATED, it means there are MORE PARTICLES in the SAME VOLUME of water (or other solvents).
Similarly, when the PRESSURE of a gas is INCREASED, it means the SAME NUMBER of particles occupies a SMALLER SPACE.
This makes COLLISIONS between the reactant particles MORE FREQUENT.
Why does INCREASING the SURFACE AREA affect the rate of reaction?
If one of the reactants is a SOLID, then breaking it up into SMALLER PIECES will INCREASE its SURFACE AREA TO VOLUME RATIO.
This means for the SAME VOLUME of the solid, the particles around it will have MORE AREA to work on - so there will be COLLISIONS MORE FREQUENTLY.
What is a CATALYST?
A CATALYST is a substance that SPEEDS UP a reaction, WITHOUT being USED UP in the reaction itself.
This means it’s NOT part of the overall reaction EQUATION.
Why does a CATALYST affect the rate of reaction?
DIFFERENT CATALYSTS are needed for DIFFERENT REACTIONS, but they all work by DECREASING the ACTIVATION ENERGY needed for the reaction to occur.
They do this by providing an ALTERNATIVE REACTION PATHWAY with a LOWER ACTIVATION ENERGY.
Why are Enzymes called BIOLOGICAL CATALYSTS?
They catalyse reactions in LIVING THINGS.
What is the rate of reaction FORMULA?
Rate of reaction = amount of reactant used or product formed divided by Time.
Name the THREE ways to measure the rate of reaction.
- PRECIPITATION and COLOUR CHANGE.
- CHANGE IN MASS (usually gas given off)
- The VOLUME of gas given off.
Describe how you could investigate the effect of increasing HCl concentration on the rate of reaction between HCl and Mg.
Add a set volume of DILUTE HYDROCHLORIC ACID to a conical flask and carefully place on MASS BALANCE.
Add some MAGNESIUM RIBBON to the acid and quickly PLUG the flask with COTTON WOOL.
By repeating this experiment, each time with MORE CONCENTRATED acid solutions and recording the mass at set intervals throughout, then it becomes clear that the MORE concentrated the FASTER the rate of reaction.
What happens if the position of Equilibrium lies to the RIGHT?
(In terms of reversible reactions)
If the equilibrium lies to the RIGHT, the concentration of PRODUCTS is GREATER than that of the reactants.
What happens if the position of Equilibrium lies to the LEFT?
(In terms of reversible reactions)
If the equilibrium lies to the LEFT, the concentration of REACTANTS is GREATER than that of the products.
What does the position of equilibrium depend on?
The POSITION OF EQUILIBRIUM depends on the following CONDITIONS (as well as the reaction itself):
- The TEMPERATURE
- The PRESSURE (this only affects equilibria involving gases)
- The CONCENTRATION of the reactants and products
When a reaction’s at equilibrium it DOESN’T mean the amounts of reactants and products are equal.
Complete the following sentence:
In reversible reactions, if the reaction is ENDOTHERMIC in one direction,…
In reversible reactions, if the reaction is ENDOTHERMIC in one direction, it will be EXOTHERMIC in the other.
