SC15 & SC16 - Dynamic Equilibria, Calculations Involving Volumes of Gases / Chemical Cells and Fuel Cells ✓

Question 1

SC15a - Through what do plants absorb mineral ions?

Answer 1

Their root hair cells

Question 2

SC15a - Why must fertilisers contain soluble compounds?

Answer 2

Root hair cells can only absorb mineral ions that are dissolved in water

Question 3

SC15a - Which three elements are featured in fertilisers?

Answer 3

• Nitrogen
• Potassium
• Phosphorus

Question 4

SC15a - What is Ammonium Nitrate an example of?

Answer 4

A Nitrogenous (Nitrogen - rich) fertiliser and a source of soluble nitrogen compounds

Question 5

SC15a - How is ammonium nitrate manufactured and how are the materials gathered?

Answer 5

Ammonium is created through the harber process. Then some ammonia is reacted with oxygen to give nitric acid and oxygen. This nitric acid is reacted with some ammonium solution. This creates ammonium nitrate:

NH3 (g) + 2O2 (g) -> HNO3 (aq) + H20 (l)

NH3 (aq) + HNO3 (aq) -> NH4NO3 (aq)

Question 6

SC15a - Where are the reactants for the harber process found?

Answer 6

• Hydrogen from natural gas

- Nitrogen from the air

Question 7

SC15a - Describe a laboratory preparation of ammonium sulfate.

Answer 7

• Small scale
• Batch process (only bit by bit)
• Ammonium solution and dilute sulfuric acid
• Titration followed by crystallisation
• Small amount made; equipment is cleaned; repeat
• Requires frequent maintenance (Hard to automate)

Question 8

SC15a - Describe a factory preparation of ammonium sulfate.

Answer 8

• Large scale
• Continuous process
• Raw materials for Ammonia and Sulfuric acid
• Several stages
• Large amount made, rarely cleaned
• Little maintenance required (Easy to automate)

Question 9

SC15a - How is sulfuric acid formed for factory preparation of ammonium sulfate?

Answer 9

• Sulfur and air are reacted to form sulfur trioxide

- Sulfur trioxide is reacted with water to from Sulfuric acid

Question 10

SC15b - How does an increase in temperature affect the position of equilibrium and rate of attainment?

Answer 10

Exothermic:
Equilibrium shifts to left 
Endothermic:
Equilibrium shifts to right
Rate of attainment increased as the particles have more energy causing more frequent collisions.

(All are opposite if temperature is decreased)

Question 11

SC15b - How does an increase in pressure affect the position of equilibrium and rate of attainment?

Answer 11

Equilibrium favors the side with fewer molecules

Rate of attainment is increased as the same amount of particles in a smaller space causes more frequent collisions

(Opposite if pressure is decreased)

Question 12

SC15b - How does an increase in concentration of the reactant affect the position of equilibrium and rate of attainment?

Answer 12

Equilibrium shifts towards the products side.

Rate of attaimment is increased as there are more particles in the same space and so there are more frequent collisions

(opposite if concentration is decreased)

Question 13

SC15b - How does a catalyst affect the position of equilibrium and rate of attainment?

Answer 13

Position of equilibrium is unaffected as it effects both sides equally

Rate of attainment is increased as the catalyst increases the rate of reaction without being used up

Question 14

SC15b - What natural occurance did the birkeland - eyde process mimick and how was this used to produce Nitric acid?

Answer 14

Lightning. An electric arc was created between two electrodes causing nitrogen to react with oxygen in the air forming nitrogen monoxide. This was then further reacted with oxygen to form nitrogen dioxide and then dissolved in water to form nitric acid

Question 15

SC15b - Why was the Birkeland - Eyde process bad?

Answer 15

• It was inefficient only producing a yield of 4% nitric acid
• It cost lots as it took up huge amounts of electricity?

Question 16

SC15b - What process do we now use to obtain Nitric Acid and how does it work?

Answer 16

The otswald process:

• Ammonia + Oxygen ⇌ Nitrogen monoxide + Water
• Nitrogen Monoxide + Oxygen ⇌ Nitrogen dioxide
• Nitrogen Dioxide + Oxygen + Water -> Nitric Acid

Question 17

SC15b - What is taken into consideration when choosing reaction pathways?

Answer 17

• availability of raw materials and energy supplies
• Rate of reaction and equilibrium position
• Atom economy, yield and usefulness of the by-products

Question 18

SC15b - What are the conditions for stage one of the Otswald Process?

Answer 18

220° and 4atm with a hot platinum catalyst

Ammonia to Nitrogen monoxide is exothermic and there are more molecules on the right

Question 19

SC16a - What are the components in a chemical cell?

Answer 19

• Two different metals each dipped in a solution of one of their own salts
• A salt (or ion) bridge to allow the ions to pass from one solution to another and complete the circuit

Question 20

SC16a - How is a potential difference created in a chemical cell and how can its strength be altered?

Answer 20

Metals push their electrons away with a certain force. The more reactive metal pushes its electrons away to the lesser reactive one which is forced to accept it. This flow of electrons creates a potential difference. Metals that have a greater difference in reactivity will create a larger potential difference. This will also create a greater current as there are more electrons flowing past one point over a given time.

Question 21

SC16a - Why may a battery go flat?

Answer 21

One of its reactants have been completely used up and so there are no more elctrons flowing past

Question 22

SC16a - What is a battery?

Answer 22

A collection of cells

Question 23

SC16a - How do rechargable batteries work?

Answer 23

They are made out of reactants that can be reformed when electricity passes through them.

Question 24

SC16a - What two elements are used in a fuel cell?

Answer 24

Hydrogen and Oxygen

Question 25

SC16a - What is used at both sides of the fuell cell to create ions?

Answer 25

Electrodes

Question 26

SC16a - What process do fuel cells mimick?

Answer 26

Photosynthesis

Question 27

SC16a - Explain how hydrogen atoms provide electricity in a fuel cell.

Answer 27

They hydrgoen fuel enters the fuel cell. Here it reaches an electrode and becomes a hydrogen ion losing its electron. The electrons move through the circuit providing a current in the circuit. The hydrogen ion passes through a water membrane to meet back with an electron and react with Oxygen atoms to form water.

Question 28

SC16a - What are the pros and cons of hydrogen-oygen fuel cells being used in cars?

Answer 28

+ Quiter and need less maintenance
- hydrogen needs to be stored carefully
+ the cell itself doesn’t release greenhouse gases
- The production of hydrogen may release greenhouse gases and also use up fossil fuels.