SC15 & SC16 - Dynamic Equilibria, Calculations Involving Volumes of Gases / Chemical Cells and Fuel Cells ✓ Flashcards
SC15a - Through what do plants absorb mineral ions?
Their root hair cells
SC15a - Why must fertilisers contain soluble compounds?
Root hair cells can only absorb mineral ions that are dissolved in water
SC15a - Which three elements are featured in fertilisers?
- Nitrogen
- Potassium
- Phosphorus
SC15a - What is Ammonium Nitrate an example of?
A Nitrogenous (Nitrogen-rich) fertiliser and a source of soluble nitrogen compounds
SC15a - How is ammonium nitrate manufactured and how are the materials gathered?
- 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)
SC15a - Where are the reactants for the Haber process found?
- Hydrogen from natural gas
- Nitrogen from the air
SC15a - Describe a laboratory preparation of ammonium sulfate.
- scale of production
- starting materials
- stages
- type of process
- maintenance
- 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
SC15a - Describe a factory preparation of ammonium sulfate.
- scale of production
- starting materials
- stages
- type of process
- maintenance
- 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
SC15a - How is sulfuric acid formed for factory preparation of ammonium sulfate?
- Sulfur and air are reacted to form sulfur trioxide
- Sulfur trioxide is reacted with water to from Sulfuric acid
SC15b - How does an increase in temperature affect the position of equilibrium and rate of attainment?
- 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)
SC15b - How does an increase in pressure affect the position of equilibrium and rate of attainment?
- 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)
SC15b - How does an increase in concentration of the reactant affect the position of equilibrium and rate of attainment?
- 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)
SC15b - How does a catalyst affect the position of equilibrium and rate of attainment?
- 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
SC15b - What natural occurance did the birkeland - eyde process mimick and how was this used to produce Nitric acid?
- 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
SC15b - What were the disadvantages of the Birkeland-Eyde process?
- It was inefficient only producing a yield of 4% nitric acid
- It cost lots as it took up huge amounts of electricity
SC15b - What process do we now use to obtain Nitric Acid and how does it work?
The Ostwald process:
- Ammonia + Oxygen ⇌ Nitrogen monoxide + Water
- Nitrogen Monoxide + Oxygen ⇌ Nitrogen dioxide
- Nitrogen Dioxide + Oxygen + Water → Nitric Acid
SC15b - What is taken into consideration when choosing reaction pathways?
- Availability of raw materials and energy supplies
- Rate of reaction and equilibrium position
- Atom economy, yield and usefulness of the by-products
SC15b - What are the conditions for stage one of the Otswald Process?
220° and 4atm with a hot platinum catalyst
(Ammonia to Nitrogen monoxide is exothermic and there are more molecules on the right)
SC16a - What are the components in a chemical cell?
- 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
SC16a - How can the strength of a chemical cell be altered?
- 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.
SC16a - Why may a battery go flat?
One of its reactants have been completely used up and so there are no more elctrons flowing past
SC16a - What is a battery?
A collection of cells
SC16a - How do rechargable batteries work?
They are made out of reactants that can be reformed when electricity passes through them.
SC16a - What two elements are used in a fuel cell?
Hydrogen and Oxygen
SC16a - What is used at both sides of the fuel cell to create ions?
Electrodes
SC16a - What process do fuel cells mimick?
Photosynthesis
SC16a - Explain how hydrogen atoms provide electricity in a fuel cell.
- 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.
SC16a - What are the pros and cons of hydrogen-oygen fuel cells?
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
