Unit 3 - Industrial Chemistry (Controlling The Rate) Flashcards
(23 cards)
What is the formula for average rate?
Average rate = change in quantity/change in time.
What is relative rate?
The rate at any one particular point in time.
What is the formula for relative rate?
Relative rate = 1/time
What unit is relative rate measured in?
s^-1.
What are the requirements for a chemical reaction to occur?
The reactant molecules must collide with sufficient energy and the correct geometry.
What is activation energy (Ea)?
The minimum kinetic energy required for a reaction to occur. This means that the reactant molecules have enough kinetic energy to collide successfully and overcome the repulsion caused by outer electrons.
What does it mean if the activation energy is high?
Only a few particles will have enough energy to collide so the reaction will be slow.
What does it mean if the activation energy is low?
The reaction will be fast as a lot of particles will have the required energy.
What is the activated complex?
- A high energy, unstable arrangement of atoms.
- Has the highest chemical potential energy in the reaction pathway.
- Formed when the reactant bonds have broken but the product bonds have not yet been formed.
What are the 5 factors that can be altered to control the rate of a reaction?
- Temperature
- Concentration
- Pressure
- Particle size
- Addition of a catalyst
What are the collisions that occur to cause a chemical change called?
Successful collisions. The greater the number of successful collisions, the faster the rate of reaction.
What is temperature?
A measure of the average kinetic energy of the particles within a substance.
What happens when temperature is increased?
The particles have more energy and so move more quickly. Increasing the temperature increases the rate of reaction because the particles collide more often.
What is concentration?
A measure of the amount of solute dissolved in a given volume of solution. A common unit of concentration is moles per litre (mol l^-1).
What happens when concentration is increased?
There are more reactant particles moving together. There will be more collisions and so the reaction rate is increased. The higher the concentration of reactants, the faster the rate of a reaction will be.
What happens to the surface area of a reactant when you decrease its size?
Surface area increases.
What happens when you increase surface area/decrease the size of the reactants?
A smaller particle size of reactants provides a greater surface area that collisions can take place on. The greater the surface area, the faster the rate of reaction.
What happens when pressure is increased?
If the pressure of gaseous reactants is increased, there are more reactant particles for a given volume. There will be more collisions and so the reaction rate is increased. The higher the pressure of reactants, the faster the rate of a reaction will be.
What is a catalyst?
- A substance that speeds up a reaction but does not take part in it, preventing it from being used up.
- Lowers the activation energy of a reaction, providing a different pathway for the particles.
- Doesn’t give the particles energy.
- Used in the chemical industry to make manufacturing processes more economical.
What happens when a catalyst is added?
- Provides a surface for reactions to take place on.
- Reactant molecules are held at a favourable angle for collisions to occur, increasing the likelihood of successful collisions.
- Allows the reaction to be carried out at a lower temperature.
- Lowers activation energy. This increases the number of molecules with the minimum kinetic energy required for a reaction to take place. This increases the number of successful collisions, thus increasing the rate of reaction.
- Does not affect the reactants or products, so the enthalpy change stays the same.
What is enthalpy?
The heat stored by a substance.
What is an exothermic reaction?
An exothermic reaction is one in which heat energy is given out. The products must have less energy than the reactants because energy has been released. The enthalpy change will always be negative.
What is an endothermic reaction?
An endothermic reaction is one in which heat energy is absorbed. The products have more enthalpy than the reactants therefore the enthalpy change is positive. Endothermic
reactions that take in energy may generate additional costs through heating the reaction to ensure that the rate remains high enough.
