Chapter 10 - Reaction rates and equilibrium Flashcards
What is the rate of a reaction?
How fast a reactant is being used up, or how quickly a product is made
What is the equation for the rate of a reaction? (mol dm^-3 sec^-1)
Change in concentration / time
Why is the rate fastest at the start of a reaction?
Each reactant is at its highest concentration
Why does the rate of reaction decrease as a reaction progresses?
The concentrations of the reactants decrease as they are used up
What are the four factors that can affect the rate of a chemical reaction?
Concentration, temperature, catalyst and surface area
What are the two characteristics of a successful collision?
The particles collide with the correct orientation
They collide with sufficient energy
What is the activation energy?
The minimum amount of kinetic energy particles need to break the bonds in the reactants and start a reaction
How does increasing the concentration of particles increase the rate of reaction?
Increasing the concentration increases the number of particles in the same volume. This means that they are closer together and so will collide much more frequently, so there are more chances to react
How does increasing the pressure of a gas increase the rate of reaction?
An increase in pressure means that volume decreases. There is, therefore, the same number of particles but in a smaller area, which means that they are closer together and successful collisions are more common
Two ways of measuring the progress of a reaction
Monitor the decrease in concentration of a reactant
Monitor the increase in the concentration of a product
How can gases be used to find the rate of reaction?
Gas collection - monitor the volume of gas produced at regular intervals
Conduct the reaction on a balance and measure the loss of mass of the reactants
How would you measure the rate of reaction of the decomposition of hydrogen peroxide?
Place the hydrogen peroxide in a conical flask attached to a gas syringe
Add some manganese dioxide, which acts as a catalyst
Record the volume of gas in the cylinder at regular intervals
When no more gas is produced, the reaction has finished
How would you work out the rate of reaction from a graph?
Draw a tangent against the curve and find the gradient
Gradient = dy / dx
This is the rate of reaction at that time
How would you measure the rate of reaction between calcium carbonate and hydrochloric acid?
Add the reactants to a conical flask, which is upon a balance
Record the mass of the flask initially and at regular intervals
The reaction is complete when no more mass is lost
What is a catalyst?
A substance that speeds up a reaction by providing an alternative route with a lower activation energy. At the end of the reaction, the catalyst is regenerated
What catalyst is used in the Haber process?
Iron
What is a homogeneous catalyst?
The catalyst and reactants are in the same states, e.g. both being aqueous
What happens when the catalyst and reactants are in the same states?
The catalyst forms an intermediary , which breaks down to form the products of the reaction
What is a heterogeneous catalyst?
The catalyst and reactants are in different states, e.g. a solid catalyst and gaseous reactants
What happens when the catalyst and the reactants are in different states?
Reactant molecules are weakly bound to the surface of the catalyst and held in the correct orientation for a reaction to take place
The catalyst in the Haber process
Iron
The catalyst in the hydrogenation of alkanes
Nickel
What is autocatalysis?
A reaction where one of the products acts as a catalyst
The reaction starts slowly and speeds up as the catalyst is formed
Why is using a catalyst beneficial for the environment?
The temperature would otherwise have to be raised a lot to make the reaction occur fast enough. The fact that less energy is used means that fewer fossil fuels are burnt and less electricity is used
