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SC15 Part 2 and SC16

QuestionAnswer
What is a by-product of an industrial process? A substance produced in a chemical reaction in addition to the desired product.
What is a system called if no substances can enter or leave it? A closed system.
What do chemists call a series of reactions used to make a particular product? A reaction pathway
If the temperature of an endothermic reversible reaction is increased what happens to the position of the equilibrium, and the time taken to reach equilibrium? The position of the equilibrium moves in the direction of the endothermic reaction, The time taken to reach equilibrium decreases.@
If the concentration of a reacting substance is increased what happens to the position of the equilibrium, and the time taken to reach equilibrium? The position of the equilibrium moves away from the reactants, The time taken to reach equilibrium decreases.
If a catalyst is added to a system in dynamic equilibrium what happens to the position of the equilibrium, and the time taken to reach equilibrium? Position of equilibrium unchanged, Time taken to reach equilibrium decreases.
If the pressure is decreased in a reversible reaction involving gases what happens to the position of the equilibrium, and the time taken to reach equilibrium? Position of equilibrium moves to side with more molecules, Time taken to reach equilibrium increases.
What do scientists call a device that produces a voltage due to reactions between reactants stored inside it, until one of the reactants is used up? A Chemical Cell
What is a fuel cell? A device that produces a voltage due to reactions involving a fuel and oxygen, for as long as these reactants are supplied.
What is the only waste product from a hydrogen oxygen fuel cell? Water.
What is a chemical cell? A unit which contains chemicals which produce electricity through a reaction
What are the main components of a chemical cell? An anode, a cathode and an electrolyte
What is an electrolyte? A solution containing ions which allows current to flow.
What does the potential difference of a cell depend on? The type of electrode and the electrolyte.
What is a battery? Two or more cells connected in series
What happens to the electrodes in a chemical cell? The more reactive metal depletes and the less reactive one increases in size.
In non-rechargeable cells, why do the chemical reactions stop over time? One of the reactants becomes used up.
How can certain cells be recharged? Applying an external electric current
How does the reactivity of the metal electrodes affect the size of the potential difference? The greater the difference in reactivity, the greater the potential difference.
What is a fuel cell? A cell which uses a fuel and oxygen (or air) to generate electricity.
What are the products in a hydrogen fuel cell? Water
State three advantages of hydrogen fuel cells Do not need to be recharged, no pollutants are produced, can be different sizes for different uses
State three disadvantages of hydrogen fuel cells Hydrogen is highly flammable, hydrogen is sometimes produced through non-renewable means, hydrogen is difficult to store
Complete the equation which occurs at the negative electrode of a hydrogen fuel cell 2H₂+4OH⁻→ 4H₂O + 4e⁻
Complete the equation which occurs at the positive electrode of a hydrogen fuel cell O₂+2H₂O→ 4OH⁻
What is the overall reaction occuring in a hydrogen fuel cell? O₂ + 2H₂ → 2H₂O
Does a hydrogen fuel cell produce greenhouse gases? yes water is a greenhouse gas
Does a hydrogen fuel cell produce any carbon emissions? no, only product Is water, but sometimes CO2 is produced making the hydrogen fuel.
Why is hydrogen difficult to store? It is a highly flammable gas so needs pressurised tanks
What other fuels can fuel cells run on? methanol