⭐️SC14, SC15, SC16 - quantitative analysis, dynamic equilibria, calc. With v. Of gases and chemical and fuel cells Flashcards
What is the actual yield?
The amount of product obtained in an actual equation
What is theoretical yield?
The maximum mass of product that can be formed from the reactant
How do you calculate the theoretical yield of a substance with a mass given?
- You need to calculate the RAMs of each substance and then multiply them
by the balancing no. - Add the unit symbols and then find the amount under the substance the question asks for
How do you calculate percentage yield?
(Actual yield / theoretical yield ) x 100
Why does an incomplete reaction not give 100% yield?
As not all the reactants are used up because the reaction has not been left for long enough, or the reaction may reach equilibrium
What are the 3 mean reasons reaction don’t give 100% yields
- reaction may be incomplete
- some product may be lost
- unwanted side reactions are taking place
Give an example where product is lost and so there isn’t a 100% yield given by a reaction
If a liquid is transferred from one container to the other, some will be left behind of the walls of the first container
Give an example where unwanted side reactions take place so there isn’t a 100% yield given by a reaction
Some reactants may react to make a different product and these side reactions compete with the main one
The higher the percentage yield of a reaction…
The more useful the reaction is
What does a high % yield mean?
That fewer raw materials are used to make the same amount of product so there’s less waste and more profit can be made
What does the atom economy show?
The % by mass of useful products formed in a reaction
What is the formula for atom economy?
(Ram of useful product/sum of rams of all the reactants )x 100
When is the atom economy 100%?
When all the atoms in the reactants are present in the product e.g. making ethanol by reacting ethene with steam
Why does the production of ethanol through fermentation of sugars like glucose have a lower atom economy?
Because carbon dioxide is formed as a by-product
What’s the atom economy for making iron in:
Fe2O3 +3CO - 2Fe + 3CO2
Give your answer to 1.dp
46%
How can the atom economy of a reaction be improved?
By finding the uses for the by-products in the reaction
What are some things chemists must consider when deciding on a reaction pathway?
Energy consumption, rate of reaction, raw materials and conditions needed to produce high yield
What raw materials are needed for fermentation to produce ethanol?
Carbohydrates - which are renewable
What raw materials are needed for reaction of ethene and steam to produce ethanol?
You need ethene which is obtained from crude oil and so is non renewable
What temperatures are needed for fermentation to produce ethanol?
30-40°C
What temperatures are needed to react ethene with steam to produce ethanol?
300°C
What pressures are needed for fermentation to produce ethanol?
Atmospheric pressure
What pressures are needed for the reaction of steam with ethene to produce ethanol?
High pressures of 60-70 atmosphere
What catalyst is needed for fermentation to produce ethanol?
Enzymes in yeast
What catalyst needed for the reaction of ethene with steam to produce ethanol?
Concentrated phosphorus acid
What’s the rate of reaction for fermentation vs reaction of ethene with steam to produce ethanol
Fermentation is slow
Ethene with steam is fast
How pure is the substance at the end
after using fermentation to produce ethanol?
Impure and must be fractionally distilled
How pure is the substance at the end
after using the reaction of ethene with steam to produce ethanol?
Pure
What is concentration?
The amount of solute dissolved in a stated volume of solution
What are the units of concentration?
g dm^-3
What is 1 dm^3 equal to?
1000cm^3
How do you convert from cm3 to dm3?
Divide by 1000
How do you find the concentration of a solution in g dm^-3?
Concentration in g dm^-3 = mass of solute in g / volume of solution in dm^3
How do you find the concentration of a solution in mol dm^-3?
Number of moles of solute/ volume of solution in dm^3
What equation relates the two types of concentration?
Concentration in mol dm^-3 = concentration in g dm^-3 / RAM of solute
What’s the concentration in mol dm^-3 of sulfuric acid in a concentration of 98 g dm^-3?
98 / 98 = 1 mol dm^-3
Find the concentration in mol dm^-3 of
A) 1.0mol of potassium chloride in 4.0 dm^-3 of solution
B) 0.15mol of copper sulphate in 250cm^3 of solution
A) 1/4 = 0.25 mol dm^-3
B) 250 / 1000 = 0.25
0.15 /0.25 = 0.6 mol dm^-3
What are acid - alkali titrations used for?
To find the exact volume of an acid that neutralises a specified volume of an alkali or vice versa
What do you need to calculate the concentration of one of the solutions in a titration?
The concentration of the other solution has to be known
What is the mole ratio?
The ratio in moles of the substances in a balanced equation
What are the steps to finding the concentration of an acid?
- Calculate the no.of moles of the solution of known v. And concentration (use concentration in mol dm^-3)
- Use balanced equation to find the no. Of moles of alkali that reacted
- Calculate concentration of the acid asked for in the question
Steps to finding concentration of an acid (short)…
Take the alkali with a volume and concentration to find moles the use that to get moles of the acid and using the given volume of the acid find the concentration
For more on titration calculations…
Check active learn and YouTube videos
What does the volume occupied by a sample of gas depend on?
The temperature, pressure and number of particles of the the gas
What are you assuming when using avogadro’s law in reactions?
That the temperature and pressure of chemicals in a reaction are the same
What does avogadro’s law state?
If temperature and pressure are the same, equal volumes of different gases contain equal numbers of molecules
What is the molar gas volume?
The volume occupied by one mole of molecules of any gas
What is the molar gas volume in dm3 and cm3?
24 dm3 or 24000 cm3
What is the formula for the volume of gas?
Volume of gas = amount of gas (mol) x molar volume (24)
What volume of gas is 0.5 mol of carbon dioxide?
0.5 x 24 = 12 dm3 at rtp
Why are the amount of gas formulae useful?
To find the masses of solids and volumes in chemical reactions
What do fertilisers do?
Replace the mineral ions needed by plants and so promote plant growth
What are important elements for fertilisers?
Nitrogen, potassium and phosphorus
Why must fertilisers be in soluble compounds?
As root hair cells only absorb mineral ions that are dissolved in water
What is ammonium nitrate?
A nitrogenous fertiliser and is a salt manufactured by reacting ammonia solution with dilute nitric acid
What’s the word and symbol equation for ammonium nitrate
Ammonia + nitric acid -> ammonium nitrate
NH3 (aq) + HNO3 (aq) -> NH4NO3 (aq)
What is the Haber process?
Where nitrogen and hydrogen react in a reversible reaction to manufacture ammonia
What is the word and symbol equation for the manufacture nitric acid from ammonia?
Ammonia + oxygen -> nitric acid + water
NH3 (g) + 2O2 (g) -> HNO3 (aq) + H2O (l)
What is ammonium sulphate?
A nitrogenous fertiliser made in the lab by reacting ammonia solution with dilute sulphuric acid
Give the word and symbol equation for ammonium sulphate
Ammonia + sulphuric acid -> ammonium sulphate
2NH3 (aq) + H2SO4 -> (NH4)2SO4 (aq)
How is the scale of production different when preparing ammonium sulphate in a lab compared to industrialy?
In a lab it’s small scale but in an industrial production it’s large scale
How are the starting materials different when preparing ammonium sulphate in a lab compared to industrialy?
In a lab you use ammonia solution and dilute sulphuric acid and in an industrial production, raw materials for making ammonia and sulphuric acid are used
How are the stages different when preparing ammonium sulphate in a lab compared to industrialy?
In lab you use titration then crystallisation but in an industrial production, you use several stages
How is the type of process different when preparing ammonium sulphate in a lab compared to industrialy?
In a lab you make by batch but in an industrial production, the process is continuous
What are the raw materials that go into the industrial process of making ammonium sulphate?
Sulphur, air, water, natural coal or gas
How is sulphur trioxide made in industrial production for ammonium sulphate?
Sulphur and air
What makes hydrogen in industrial production of ammonium sulphate?
Water and natural gas
What makes nitrogen in industrial production of ammonium sulphate?
Hydrogen and air
What makes sulphuric acid is industrial production of ammonium sulphate?
Sulphur trioxide and water
What makes ammonia in industrial production of ammonium sulphate?
Hydrogen and nitrogen
What is a continuous process?
Where reactants are continuously fed into the reactors and products are removed with the process rarely stopped
Why aren’t batch processes used in industrial production?
As batch processes are hard to automate and so require more people to make a given product than continuous processes which are automated
When do reversible reactions reach equilibrium?
When they’re in a closed system where no substances can enter or leave
In a dynamic equilibrium:
- The forward and backward reactions still happen at the same rate
- the concentrations of all reacting substances don’t change
If the temperature is increased, how is the position of equilibrium and time take to reach equilibrium effected?
Position of equilibrium moves in the direction of the endothermic reaction
And time taken to reach equilibrium decreases
If the pressure is increased, how is the position of equilibrium and time take to reach equilibrium effected?
Position of equilibrium moves towards the side of the balanced equation with fewer molecules of reacting gas and time taken to reach equilibrium decreases
If the concentration of a reacting substance is increased, how is the position of equilibrium and time take to reach equilibrium effected?
Position of equilibrium moves away from the reacting substance in the balanced equation and the time taken to reach equilibrium decreases
If a catalyst is added , how is the position of equilibrium and time take to reach equilibrium effected?
The position of equilibrium doesn’t change and the time taken to reach equilibrium decreases
How may chemical manufactures make a profit?
Make a compromise on yield and time taken and may mean reactions aren’t allowed to reach equilibrium
Why do chemical manufacturers make compromises when producing product?
As it’s not profitable if it takes years to reach equilibrium and choosing conditions that give a high rate of reaction isn’t worthwhile if it’s too expensive
What is the Haber process and give a symbol equation
Where nitrogen and hydrogen react to produce ammonia:
N2(g) + 3H2(g) ⇌ 2NH3(g)
Where does the equilibrium move if pressure is increased in the Haber process?
The the right
What effect do high pressures have on the Haber process?
Increase yield of ammonia and increase the rate of the reaction
What pressure is used in the Haber proces?
200 atmospheres as any higher and it becomes too expensive to maintain
What part of the Haber process is exothermic and endothermic?
Forward reaction is exothermic and backward reaction is endothermic
What temp is used in the Haber process and what happens when the temp is increased?
The position of the equilibrium moves to the left in the direction if the endothermic reaction.
Temp used is 450°C
Why doesn’t the Haber process use very high or low temperatures?
As too high temperatures mean the yeild of ammonia is reduced and too low temperatures mean the rate of reaction is reduced
What factors does the reaction pathway take into account?
- atom economy and yield and usefulness of by products
- cost and availability of raw materials
- rate of reaction and the equilibrium position
What process makes nitric acid today?
The Ostwald process
What are chemical cells?
Every day batteries used in phones and torches e.c.t
What components make up a simple chemical cell?
- two different metals each dipped into a solution of one of their salts
- a ‘salt bridge’
What is the ‘salt bridge’ in a chemical cell for?
To allow dissolved ions to pass from one solution to another
What is another word for voltage?
Potential difference
What determines wether the voltage between two metals is great?
If they are both far apart in the reactivity series
What’s the overall reaction that happens in a Daniel cell?
Zinc + copper sulphate -> zinc sulphate + copper
Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)
What kind of reaction is in a Daniell cell?
Exothermic reaction but energy is mainly transferred by electricity rather than by heating
Why do batteries go flat?
As when one of the reactants is used up, the reaction stops and a voltage is no longer produced
What’s the difference between fuel cells and chemical cells?
Chemical cells store all their reactants but fuel cells are supplied with fuel and oxygen from outside and also fuel cells don’t go flat
What do hydrogen-oxygen fuel cells use?
Use hydrogen and oxygen and produce water as the only product
What happens at the left hand electrons of a fuel cell and include a half equation?
Hydrogen atoms loose electrons and form hydrogen ions:
2H2 (g) -> 4H+ (aq) + 4e-
How do electrons get to the positive electrode of a fuel cell?
Electrons Flow through the eternal circuit and hydrogen ions pass through a membrane to the right hand electrode
What happens at the right hand electrode of a fuel cell? Include a half equation.
Hydrogen ions gain electrons and react with oxygen
4H+ (aq) + 4e- + O2 (g) -> 2H2O (g)
What is the positives of a hydrogen-oxygen fuel cell in comparison to a petrol or Diesel engine?
Much quieter, less maintenance and don’t produce CO2
What is a negative of a hydrogen-oxygen fuel cell?
The actual manufacture of hydrogen releases CO2 as a by-product due to the reaction of steam with coal or natural gas
What are the electrodes of a fuel cell made of?
Platinum
What is between the electrodes of a fuel cell?
A membrane which lets hydrogen ions pass but not electrons
