paper 2 Flashcards
Collision theory
chemical reactions can only take place then the reacting particles collide with each other. The collisions must have sufficient energy
rate of reaction
frequency of successful collisions
what does inc conc mean on amount produced and ror
inc ror as more collisions, more product as there are originally more reactants
hypothesis
proposal that could explain a fat or an observation- must be testable
2 ways of required practical for ror. And give the problem for it
- Using a measuring cylinder, put 10cm^3 of sodium thiosulfate solution into a conical flask
- Place flask onto a printed black cross
- Add 10 cm^3 of HCl into the conical flask
- Swirl and start a stopwatch
- Look down through the top of the flask and after a certain time, the solution will go cloudy.
- Stop clocl when we can no longer see the cross
- Carry out the experiment again but with a lower conc of sodium thiosulfate solution
- Repeat the whole experiment and calculaate mean values for each conc of sodium thiosulfate solution. -don’t include any anomolous results
PROBLEM: different people have different eyesight= practical is not producible
Other way:
- Use measuring cyclinder to place 50 cm^3 of HCl in conical flask
- Attach conical flask to a bung and delivery tube
- Place delivery tube into a container filled with water.
- Place upturned measuring cylinder also filled with water over delivery tube
- Add 3cm strip of magnesium to HCl and start a stopwatch
- reaction produces hydrogen gas which is trapped in the measuring cylinder. - Every 10 seconds, measure the volume of hydrogen gas in the measuring cylinder and continue until no more is given off
- Repeat experiment using different conc of HCl
What does it mean if a measurement is reproducible?
It can be repeated by another person or using a different technique or equipment and still get the same results
If there is a smaller sized block, what does this mean?
It has a greater surface to volume ration than larger blocks
Why is cotton wool used at the top of conical flasks in most practicals?
To allow the gas to escape but not the liquid
activation energy
The minimum amount of energy that the particles must have in order to react (i.e. collide successfully)
measure for mass and volume
Mass= grams Volume= cm^3
measure for ror
g/s or cm^3/s
why does increasing temp inc ror?
Because it increases the energy of the particles and because of this, they move faster which increases the frequency of collisions. Also means that more particles can overcome the activation energy barrier and collide successfully.
Catalyst: what it is, why it is important and how it increases increases the rate of reaction
Increases the rate of chemical reactions but are note used up during the reaction. Different reactions need different catalysts.
- Important because they allow us to carry out reactions without needing to increase the temperature. This save money.
- Catalysts increase the rate of reaction by providing a different pathway for the reaction that has a lower activation energy
when is eq reached?
When the forwards and reverse reaction occurs at the same rate in a CLOSE system and a reversible reaction
La Chatelier’s principle
If a system is at eq and a change is made to the condition, then the system will counteract the change
what happens if the conc of the product decreases?
Then more reactant will react to form more of the product until eq is reached again
What happens to eq when conc of reactant incs
More product will be formed until eq is reached again
When happens to eq when there is an increase in temperature
EQ will shift with the endothermic side to decrease the temperature because it causes energy to be take in, causing the temperature to fall back to it’s original temp
what happens to eq when there is a decrease in temp?
Eq will shift towards the exothermic die as it causes energy to be released there increasing temp back to normal
what happens to eq when you increase pressure?
EQ shifts to the side with the smaller numer of molecules (talking about the big number beofre the equation.
What happens to eq when pressure decreases
EQ shifts to the side with the highest number of molecules-
What is a hydrocarbon
molecules made up of hydrogen and carbon atoms only
Equation for methan
CH4
Equation for Ethane
C2H6
Equation for propane
C3H8
Equation for Butane
C4H10
general formula for alkanes
CnH2n+2
why are alkanes saturated molecules?
Because the carbon atoms are fully bonded to hydrogen atoms by single bonds
Describe the flammability, viscosity and bp as you increase the size of the hydrocarbon
Flammability- as hydrocarbon molecules increase, the molecules get less flammable
Viscosity- as the size of the hydrocarbon molecules increases, the molecules et more viscous
BP- as you increase the size of the hydrocarbon, the boiling point incs
How do you release energy by using hydrocarbons
Combust them/ burn them
What happens during the combustion of hydrocarbobs
The hydrogen and carbons atoms in the fuel react with oxygen, The carbon and hydrogen are oxidised.
what is the formula for complete combustion and when does it happen
it happens when there is an unlimited/ not a lack of oxygen. Formula- CH4 + O2 —> CO2 + H2O
When does incomplete combustion occur and give the two equations for it. And also explain the negative effects of the products of it
Occurs when there is a poor supply of O2. Formulas:
- CH4 + O2 –> CO + C + H2O
- CH4 + O2 –> C + H2O
C (soot): causes breathing problems and also reduces the amount of solar energy received= global dimming
CO (carbon monoxide): Toxic, absorbed in the lungs and binds with haemoglobin in red blood cells which means that there is a lower capacity in how much oxygen it can carry
Give all of the stages in fractional distillation
- Crude oil is heated to a very high temperature= crude oil boils
- Crude oil vapour is now fed into the fractional distillation column- column is hot at the bottom and cooler at the top
- Hydrocarbons rise up the column- and condense when they reach their boiling point
- Remaining hydrocarbons continue moving up the column
- add the extra details in the exam