Rates, equilibrium, and organic chemistry
What does the rate of reaction tell you?
How fast the reactants turn into products
What are the two ways of working out a rate of reaction?
The decrease in the reactant or the increase in the product in a certain amount of time
Describe an experiment to show the loss of mass in a reactant
1. Put a conical flask filled with marble chips on a top-pan balance
2. Add the hydrochloric acid into the conical flask and quickly add the cotton wool bung and read the weight
3. Read and record the weight every 1 minute until there is no longer a decrease in mass
Why do you put the cotton wool bung on top of the conical flask when you are reacting hydrochloric acid and marble chips
To stop the acid splashing out, but allowing the carbon dioxide to escape out
How do you calculate the rate of reaction of a curve?
1. Draw a tangent to the curve at that time that just touches the curve at that point
2. Then construct a right angled triangle using the tangent as your longest side
3. Find the difference of the two tips of the longest side on the y axis
4. Find the different from the bottom two angles of the triangle on the x axis
5. Divide the difference in y over the difference in x
6. This will give you your rate of reaction
Describe the experiment of measuring the volume of gas given off.
1. Add marble chips and hydrochloric acid into a conical flask
2. Quickly add the bung which has a delivery tube into the gas syringe
3. After each minute record the volume of gas in the gas syringe and record in a table
4. After there is no more gas produced you know that one reactant is in excess and there will be no more reacting and you can stop the experiment
Describe the experiment of what happens hen you change the temperature in a reaction
1. Measure 10cm cubed of hydrochloric acid and another 10cm cubed of sodium thiosulphate in separate clean measuring cylinders
2. Choose temperature to investigate and use and ice bath or hot water bath to get the two solutions up to the right temperature
3. Place the flask on the centre of the large cross; first add the sodium thiosulphate to the flask then add the hydrochloric acid and start the stopwatch and swirl the mixtures
4. Stop the clock when the cross disappears and note the time
Repeat with different temperatures
What are the two different calculations you can do to work out the mean rate of reaction?
quantity of reactant used quantity of product formed
—————————— or —————————–
If the gradient of a reaction line is steeper is the reaction time faster or slower?
What does the gradient of the line at any given time on a graph tell you?
The rate of reaction at that time
What are the five main factors that affect the rate of reaction?
Temperature, surface area of solids, concentration of solutions, pressure of gases and whether a catalyst is present
Describe the collision theory
When particles collide with enough energy to cause a reaction ( having the activation energy)
What is the activation energy?
The minimum amount of energy that particles must have before they can react
Name two things that will increase the likeliness for a successful reaction
– Increase the frequency of reacting particles colliding with each other
– Increase the energy they have when they collide
If you increase the chance of particles reacting do you increase or decrease the rate of reaction?
Increase the rate of reaction
Why does something react more slowly if it has a smaller surface area?
Because the particles inside a large lump of solid are not in contact with reactant with the reactant particles of the solution, so they cannot react. The particles inside the solid have to wait for the particles on the surface to react first before they are exposed and have a chance to react
Why is the rate of reaction faster when the solid has a larger surface area?
Many more particles of the solid are exposed and able to react at a given time. This means that reactions can take place much more quickly
Why does an increase in temperature result in an increase of rat of reaction?
An increase in temperature means the particles have more energy and so they move around more and collide more often creating more successful reactions. The increase in energy also means a higher proportion of particles have energy greater than the activation energy so more successful reactions take place.
Does increasing the concentration of a solution increase or decrease the rate of reaction?
Increases the rate of reaction
Does increasing of pressure of reacting gases increase or decrease the rate of reaction?
Increases the rate of reaction
Why does increasing the concentration increase the rate of reaction?
Because there are more reactant particles in the same volume of solution. The more ‘crowded together’ the reactants particles are, the more likely they are to collide increasing the rate of reaction
Why does increasing the pressure of reacting gases increase the rate of reaction?
Increased pressure squashes the gas particles more closely together. There is more chance of collision between the particles.
What is a catalyst?
A substance that changes rate of reaction however is not changed chemically itself and remains he same at the end of a reaction