C7
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- Created by: sophielouise277
- Created on: 10-10-18 19:53
What is an exothermic reaction?
A reaction which transfers energy from the reacting chemicals to their surroundings
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How can you tell it is an exothermic reaction?
There is a rise in temperature
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What are some examples of exothermic reactions?
Combustion of methane gas and neutralisation reactions
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What do the products of an exothermic reaction have?
A lower energy content than in the reactants
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Where can you use exothermic reactions in everyday life?
Hand and body warmers
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What is the chemical reaction in single use hand warmers?
Iron turns into hydrated Iron(III) oxide
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What is used as a catalyst in this reaction?
Sodium Chloride
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What are reusable hand-warmers based on?
Formation of crystals from solutions of a salt
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What is the salt used?
Sodium ethanoate
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How does this work?
A supersaturated solution is prepared by dissolving as much of the salt as possible in hot water. Then allowed to cool
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What is the purpose of the metal disk?
A small particles of metal are scarped off which starts of the crystallisation
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What is another use of exothermic reactions?
In self heating cans
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What is the reaction that is usually used to transfer energy to the food or drink?
calcium oxide+water= calcium hydroxide
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How does the reaction work?
You press a button which breaks the seal and allows the two to mix
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What is the reaction profile for an exothermic reaction?
*
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What is an endothermic reaction?
A reaction which transfers energy from the surroundings to the reacting chemicals
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How can you know if it is an endothermic reaction?
Fall in temperature
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What are some examples of endothermic reactions?
Citric acid + sodium hydrogenate and thermal decomposition
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What do the products of an endothermic reaction have?
Products have a higher energy content than the reactants
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What is a use for endothermic reactions in real life?
Chemical cold packs
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What is the reaction that happens in a chemical cold pack?
Ammonium nitrate dissolves in water which absorbs energy
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How do you make the reaction happen?
You squeeze the bag and ammonium nitrate is released
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What is the reaction profile for endothermic reactions?
*
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What is activation energy?
Minimum amount of energy needed before colliding particles of reactants have sufficient energy to cause a reaction
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What is breaking bonds?
An endothermic reaction
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What is forming new bonds?
Exothermic
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What is bond energy?
Energy needed to break the bond between atoms
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How to calculate energy change in a reaction?
How much energy needed and how much energy released
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What is the rule between reactivity and voltage?
The greater in difference in reactivity between the two metals used, the higher the voltage produced
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What happens when two metals are dipped in a salt solution and joined by a wire?
The more reactive metal will donate electrons to the less reactive metal
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What happens in non rechargeable batteries?
Once one reactant tuns out, the cell stops working
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How do rechargeable batteries work?
When connected to a power supply the reactions are reversed at each electrode
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What is the formula for hydrogen and oxygen?
Hydrogen + oxygen = water
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What could using hydrogen as fuel reduce?
Global warming
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What are the problems of using hydrogen as a fuel?
Safety and storage that need to be solved, supplying the hydrogen to burn in car engines and making hydrogen using electrolysis requires energy from fossil fuels.
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What is a fuel cell?
A more efficient way of using the energy from oxidising hydrogen
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What happens at the negative electrode in a fuel cell?
*
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What happens at the positive electrode in a fuel cell?
*
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What is the overall reaction inside a fuel cell?
*
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What are the three advantages of fuel cells?
No electric recharge, no pollutants, range of sizes
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What are the three disadvantages of fuel cells?
Hydrogen is flammable, hydrogen sometimes produced for cell by non renewable sources and hydrogen is difficult to store
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Other cards in this set
Card 2
Front
How can you tell it is an exothermic reaction?
Back
There is a rise in temperature
Card 3
Front
What are some examples of exothermic reactions?
Back
Card 4
Front
What do the products of an exothermic reaction have?
Back
Card 5
Front
Where can you use exothermic reactions in everyday life?
Back
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