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 Haber 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) + H₂O (l)
• NH₃ (aq) + HNO₃ (aq) →NH₄NO₃ (aq)

Question 6

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

Answer 6

• Hydrogen from natural gas
• Nitrogen from the air

Question 7

SC15a - Describe a laboratory preparation of ammonium sulfate.

• scale of production
• starting materials
• stages
• type of process
• maintenance

Answer 7

• scale of production - small
• starting materials - ammonia solution and dilute sulfuric acid
• stages - titration followed by crystallisation
• type of process - batch process
• maintenance -apparatus must be cleaned regularly - difficult to automate

Question 8

SC15a - Describe a factory preparation of ammonium sulfate.

• scale of production
• starting materials
• stages
• type of process
• maintenance

Answer 8

• scale of production - large
• starting materials - raw materials for making ammonia and sulfuric acid
• stages - several stages
• type of process - continuous
• maintenance - only stopped rarely to maintain and clean equipment

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

• Equilibrium shifts in the endothermic direction
• 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 - What were the disadvantages of the Birkeland-Eyde process?

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 Ostwald 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 can the strength of a chemical cell be altered?

Answer 20

• 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 fuel 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

• The 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?

Answer 28

Pros:

• Quiter and need less maintenance in a petrol or diesel engine
• The cell itself doesn’t release greenhouse gases

Cons:

• The production of hydrogen may release greenhouse gases and also use up fossil fuels.
• Hydrogen needs to be stored carefully as it can explode