C5 - monitoring and controlling chemical reactions Flashcards
1
Q
what is a mole?
A
a mole is an amount of substance which contains 6.02x10^23 elementary entities
2
Q
what are three equations which involve moles?
A
- m = n x Mr
- no. of particles = n x avogadros constant
- n = c x (v/1000)
3
Q
what are some different ways to measure the volume of gas given off during a reaction?
A
- inverted measuring cylinder
- burette
- gas syringe
- pan-top balance (mass loss)
4
Q
how many cm^3 are in 1 dm^3?
A
1000
5
Q
what volume does 1 mole of any gas occupy at room temperature and pressure?
A
24dm^3
6
Q
what is the molar volume?
A
the volume that 1 mole of any gas occupies at room temperature and pressure (24dm^3)
7
Q
how can number of moles be calculated with volume?
A
number of moles = volume/24
8
Q
what type of reaction is CaCO3 -> CaO + CO2?
A
thermal decomposition reaction
9
Q
why wouldn’t a reaction make 100% of the theoretical yield?
A
- system may be at equilibrium (reversible)
- may have impure starting reactants
- may lose reactants and/or products during manufacturing process e.g. during filtration
- side reactions may occur
10
Q
how is percentage yield calculated?
A
(actual yield/theoretical yield) x 100
11
Q
what is atom economy?
A
- a way of measuring how many atoms from the reactants are used to make the products
12
Q
what does 100% atom economy mean?
A
all the atoms in the reactants are used in forming the products e.g. the Haber Process
13
Q
what is high atom economy better for?
A
profits and the environment
14
Q
what’s bad about reactions with low atom economies?
A
- they use up resources very quickly
- make lots of waste materials that have to be disposed of
- tend to be unsustainable
15
Q
why are low atom economy reactions usually not profitable?
A
- raw materials can be expensive to buy
- waste products can be expensive to remove and dispose of responsibly
16
Q
what is the atom economy if there’s only 1 product?
A
100%
17
Q
how is atom economy calculated?
A
(Mr of useful product/Mr of all products) x 100
18
Q
what is a solute?
A
a substance that dissolves in a solvent
19
Q
what is a solvent?
A
a substance that can dissolve a solute to form a solution
20
Q
what is a solution?
A
a mixture formed when one substance dissolves into another
21
Q
what is concentration?
A
a measure of how much solute is in a given volume of solution; it can be measured in g/dm^3 or mol/dm^3
22
Q
how do you convert g/dm^3 to mol/dm^3?
A
divide by Mr
23
Q
how do you convert mol/dm^3 to g/dm^3?
A
multiply by Mr
24
Q
how do you convert cm^3 to dm^3?
A
divide by 1000
25
how do you convert dm^3 to cm^3?
multiply by 1000
26
how many litres/ml in 1 dm^3?
1 dm^3 = 1 litre = 1000ml
27
what is the difference between strength and concentration in acids?
- concentration tells us how many moles of acid there are per litre
- strength tells us how much it ionises
28
how are pH and H ^+ concentration related?
- as hydrogen ion concentration increases by a factor of 10, the pH value of a solution decreases by a factor of 1
29
what is a titration?
a titration is a practical in which we measure exactly what volume of two solutions will react together i.e. measuring the volume of acid needed to neutralise a measure of volume of alkali
30
what is the endpoint?
- the point where a reaction finishes (when the indicator changes colour)
31
how is the endpoint observed?
using a suitable indicator (for acid-base titrations, this is where the pH reaches 7/neutral)
32
what is a standard solution?
any solution that you know the concentration of
33
what are titrations used to find out?
concentrations
34
how is a titration carried out?
1. using a pipette, measure out a set volume of the alkali into a flask; add a few drops of an indicator (usually phenolphthalein or methyl orange)
2. fill a burette with a standard solution (a known concentration) of acid
3. use the burette to add the acid to the alkali a bit at a time; swirl the flask regularly; go slowly (a drop at a time) when the alkali's almost neutralised
4. the indicator changes colour when all the alkali has been neutralised (this is called the endpoint)
5. record the volume of acid used to neutralise the alkali
6 repeat process a few times, ensuring very similar results each time and calculate mean
35
what colour is phenolphthalein in alkalis and acids?
- pink in alkalis
- colourless in acids
36
what colour is methyl orange in alkalis and acids?
- yellow in alkalis
- red in acids
37
why is universal indicator not used in titrations?
it changes colour gradually and we want a single colour change
38
where should you keep the burette while you fill it?
eye level/below eye level
(don't want to be looking up if any acid spills)
39
how do you work out when the alkali is neutralised in a titration?
- do a rough titration first
- note approx. amount of acid needed, then go slowly as you get near the amount on the next run
40
what factors need to be considered in industry?
- atom economy
- percentage yield
- rate of reaction
- whether reaction is reversible
41
what is the volume occupied by one mole of a gas known as?
the molar volume
42
how do we calculate molar volume?
molar volume = gas volume/number of moles
43
what equation links volume to moles?
volume = moles x 24
44
what does percentage yield compare?
actual and predicted yield
45
how can we tell a reaction has occurred?
- effervescence
- colour change
- change in mass
- change in energy (temperature)
46
what factors can affect rate of a reaction?
- temperature
- concentration (for aqueous reactants)
- pressure (gaseous reactants)
- catalysts
- surface area
47
what is the rate of anything?
how much of it happens in a given time
48
what is the rate of reaction?
how much of the reaction occurs per unit of time; usually measure grams of product made or reactant used
49
what is an equation for rate of reaction?
rate of reaction = amount of product formed/time taken
50
when do reactions take place?
when particles collide with a certain amount of energy
51
what is the activation energy?
the minimum energy needed for the particles to react successfully
52
what happens if particles collide with less energy than the activation energy?
they will not react (just bounce off eachother)
53
what effect does temperature have on the rate of a reaction?
- a higher temperature means that particles have more kinetic energy so hey move faster
- so they collide with more force, so more particles have enough energy to overcome activation energy
- leading to more frequent successful collisions or increase collision frequency
54
how does concentration or gas pressure affect the rate of reaction?
- higher concentration or gas pressure will increase number of particles present in a set volume
- causing increased collision frequency and increased rate of reaction as more collisions exceed activation energy
55
how does surface area affect the rate of reaction?
- increased surface area will increase number of particles available to react
- leading to increased collision frequency
56
what is a catalyst?
increases rate of reaction by providing either a surface on which the reaction can occur, or by providing a different reaction pathway; by lowering activation energy
57
what are some common catalysts?
- iron
- platinum
- vanadium (V) oxide
58
what reaction does iron catalyse?
making ammonia from nitrogen and hydrogen
59
what reaction does platinum catalyse?
making nitric acid from ammonia
60
what reaction does vanadium (V) oxide catalyse?
making sulphuric acid
61
is the catalyst used up in a reaction?
no
62
how do catalysts work?
a catalyst lowers activation energy
- a greater proportion of colliding particles now have enough energy to react
- therefore the rate of successful collisions increases
63
how could you experiment to find out if a particular solid could be a catalyst for a reaction?
- measure the reaction rate without the solid present and then again with a known mass of the solid added
- if the rate increases, but the solid appears to be unchanged, it could be a catalyst
- you can check that none of the solid has been used up by filtering it out at the end, drying it and measuring the mass to check it's all still there
64
what are some key aspects of dynamic equilibrium?
- the rate of the forward reaction equals the rate of the backward reaction
- concentrations of the products and reactants remain
65
if a reversible reaction is exothermic in one direction, what is it in the other direction?
endothermic
66
when is equilibrium reached?
when the forward and reverse reactions occur at exactly the same rate
67
what might affect a reaction in equilibrium?
- temperature
- pressure
- concentration
68
what is le chatelier's principle?
describes how the position of equilibria changes to favour the forward or backward reaction
69
what happens to the position of equilibrium if the temperature increases?
if the temperature increases the reaction will shift to favour the side that will reduce the temperature (the endothermic side)
70
what happens to the position of equilibrium if the concentration increases on one side?
if the concentration increases on one side they are more likely to react together shifting the equilibrium so the concentration decreases
71
what happens to the position of equilibrium if the pressure increases?
increasing the pressure shifts the reaction to favour the reaction that produces a smaller number of products; increasing pressure favours the side of the equation with the least gas molecules
72
what is sulphuric acid used for/in?
- car batteries
- as an oxidising agent
- ore processing
- waste processing
73
what is the name of the process in which sulphuric acid is made?
the contact process
74
what are some optimum conditions used to create more sulphur trioxide in the contact process?
- 450 degrees celsius
- atmospheric pressure (1atm)
- the catalyst vanadium (V) pentoxide
