Topic 5- Energy Changes Flashcards Preview

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Flashcards in Topic 5- Energy Changes Deck (17):

What is an exothermic reaction?

It is the one that transfers energy to the surroundings, usually by heating. (Shown by rise of temperature)

Heat is given out...

-bond forming


What is combustion?

It is like burning a fuel, like exothermic reaction..(it gives out lot of energy)


Is neutralisation exothermic?

Yes, (also many oxidation reaction are exothermic)


What are the examples of everyday uses of exothermic reaction ?

-hand warmers : (exothermic oxidation of iron in air with salt solution catalyst) to release energy.

-self heating cans (hot choc or coffee)


What is an endothermic reaction?

It is the one which takes in energy from the surroundings. ( It is show by a fall of temperature).

-bond breaking


What are the everyday uses of endothermic reaction?

They are used in sports injury pack ( the chemical reaction allows the pack to become instantly cooler without any freezer)


What are reaction profiles?

They are the diagrams that show the relative energies of the reactant and products in a reaction, and how the energy changes over the course of the reaction.


How would an exothermic reaction would look on the reaction profile....

Starts (Reactants) top , end (product) bottom...

-activation energy points up
-energy released points down


Endothermic reaction on the reaction profile....

Starts (Reactants) bottom , end (product) top...

-activation energy points up
-energy absorbed points up


What is an electrochemical cell?

It is a basic system made up of two different electrodes in contact with an electrolyte.

-the two electrodes must be able to conduct electricity and so are usually metals.


What is an electrolyte?

It is a liquid that contains ions that react with the electrodes.


The bigger the difference in reactivity of the electrodes...

The bigger the voltage of the cell.


What happens in a non-rechargeable batteries....

-reactants get used up
-they contain cells which use irreversible reactions.


How in a rechargeable cell, the reactions can be reversed?

By connecting it to an external electric current.


What is an fuel cell?

It is an electrical cell that's supplied with a fuel and oxygen and uses energy from the reaction between them to produce electrical energy efficiently.


What happens when the fuel enters the cell?

It becomes oxidised and sets up a potential difference within a cell


What happens in the hydrogen-oxygen fuel cell?

The fuel cell combines hydrogen and oxygen to produce nice clean water and release energy.