Kinetics, Equilibria and Redox Reactions Flashcards
What is the equation for rate of reaction?
Amount of reactant used or product formed / time
What are two things that need to happen for a reaction to take place between two particles?
-Need to collide in the right direction - need to be facing each other in the right way
-They collide with at least a certain minimum amount of kinetic energy
What is activation energy?
The minimum amount of kinetic energy that particles need to react
What does the peak of a Maxwell-Boltzmann Distribution graph represent?
The most likely energy of any single molecule
What is the area under Maxwell-Boltzmann Distribution curve?
Equal to the total number of molecules
Why does the Maxwell-Boltzmann Distribution curve start at 0,0?
No molecules have zero energy
What it at the right of the peak of a Maxwell-Boltzmann Distribution curve?
The mean energy of all the molecules
What happens to the particles in a reaction if you increase temperature? How does this change the Maxwell-Boltzmann distribution curve?
If you increase the temperature of a reaction, the particles will on average have more kinetic energy and will move faster.
So, a greater proportion of molecules will have at least the activation energy and will be able to react
This changes the shape of the Maxwell-Boltzmann distribution curve - pushed it over to the right
Small increase in temperature can lead to quite a large increase in reaction rate
What is a catalyst?
A substance that increases the rate of reaction by providing an alternative reaction pathway with a lower activation energy
The catalyst is chemically unchanged at the end of the reaction
What are the three ways of measuring reaction rates?
Timing how long a precipitate takes to form
Measuring a decrease in mass
Measuring the volume of gas given off
How do you time how long a precipitate takes to form when measuring reaction rates?
1) You can use this method when the product is a precipitate which clouds a solution
2) You watch a mark through the solution and time how long it takes to be obscured
3) If the same observer uses the same mark each time, you can compare the rates of reaction, because roughly the same precipitate will have been formed when the mark becomes obscured
4) But this method is subjective - different people might not agree on the exact moment the mark disappears
How do you measure a decrease in mass when measuring reaction rates?
1) When one or more of the products is a gas, you can measure the rate of formation using a mass balance
2) As gas is given off, the mass of the reaction mixture decreases
3) This method is accurate and easy to do. But it does release gas into the atmosphere, so it’s usually done in a fume cupboard
How do you measure the volume of gas given off when measuring reaction rates?
1) This involves using a gas syringe to measure the volume of gas being produced
2) You can only use this method when one or more of the products is a gas
3) Gas syringes usually give volumes to the nearest 0.1cm3, so this method is accurate
Describe the method of the reaction between Sodium Thiosulfate and Hydrochloric acid?
Both are clear colourless solutions which react together to form a yellow precipitate of sulfur
1) Measure out fixed volumes of sodium thiosulfate and HCl, using a measuring cylinder
2) Use a water bath to gently heat both solutions to desired temperature before you mix them
3) Mix the solutions in a conical flask. Place the flask over a black cross which can be seen through the solution. Watch the black cross disappear through the cloud sulfur and time how long it takes to go
4) The reaction can be repeated for solutions at different temperatures. The depth of liquid must be kept the same each time. The concentrations of the solutions must also be kept the same
5) The results should show that the higher the temperature, the faster the reaction rate and therefore the less time it takes for the mark to disappear
What happens to the reaction when reactants get used up?
Forward reaction slows down
What happens to the reaction when more product is formed?
Reverse reaction speeds up
What is dynamic equilibrium?
The concentrations of reactants and products stay constant
Can only happen in a closed system
What happens if the position of equilibrium moves to the left?
You get more reactants
What happens if the position of equilibrium moves to the right?
You get more products
