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UK GCSE Chemistry > Energy Change (C5) > Flashcards

Energy Change (C5) Flashcards

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1
Q

Describe an Endothermic reaction

A

The reactants take in energy from the surroundings during the reaction

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2
Q

Describe an Exothermic reaction

A

The reactants give out energy to the surroundings during the reaction

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3
Q

What happens during any reaction?

A

Bonds are made or broken

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4
Q

What happpens when bonds are broken?

A

Energy is taken in (endothermic)

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5
Q

What happpens when bonds are made?

A

Energy is released (exothermic)

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6
Q

Examples of exothermic reations

A

Combustion
Neutralisation
Oxidation

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7
Q

Examples of endothermic reactions

A

Reaction between citric acid and sodium hydrogen carbonate (i.e.: lemon juice and baking soda)
Thermal Decomposition

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8
Q

Describe the reaction profile of an endothermic reaction

A

The energy increases to the activation energy and then falls a bit but not as low as the original reactants.

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9
Q

Describe the reaction profile of an exothermic reaction

A

The energy increases to the activation energy and then falls lower than the original reactants.

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10
Q

What is the heighest point on the reaction profile?

A

Activation Energy

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11
Q

What is the activation energy?

A

The minimum amount of energy the particles need when colliding to react.

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12
Q

How can we measure the amount of energy released by a chemical reaction?

A

Take the temperature of the reactants, mix them in a polyester cup and measuring the temperature at the end of the reaction

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13
Q

What is the biggest problem with measuring energy released from a chemical reaction using a polyester cup and how can it be reduced?

A

A lot of energy is lost to the surroundings

It can be reduced by placing a lid on the cup and insulating it with cotton wool

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14
Q

What variables must be controlled when investigating energy transferred in a reaction?

A

Mass
Concentration
How often the tempreature is taken

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15
Q

In a bond energy equation, if the answer is positive it means that…

A

More energy was taken in than released (endothermic)

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16
Q

In a bond energy equation, if the answer is negative it means that…

A

More energy was released than taken in (endothermic)

17
Q

What are electrochemical cells?

A

A basic system by which chemical reactions create electricity

18
Q

How do electrochemical cells work?

A

Two electroldes are in an electrolyte with ions which are reacting and go to either pole
The two electrolytes are connected by a wire and thus the delocalised electrons flow through

19
Q

What changes the charge or voltage of a cell?

A

Type of electrode

Type of electrolyte

20
Q

The greater the difference in reactivity of the electrodes….

A

…the greater the voltage of the cell

21
Q

What is a battery?

A

Two combined cells

22
Q

What is the voltage of any given battery?

A

The sum of the voltage of its individual cells

23
Q

What does it mean if a battery is non-rechargable?

A

The chemical reactions that occur at the electrodes are IRREVERSABLE and so the reactants are eventually used up

24
Q

What type of batteries are alkaline batteries?

A

Non-rechargable

25
Q

How do rechargable batteries work?

A

The reaction is reversible so when hooked up to an external electric current it is reversed and the reactants can be re-used

26
Q

Describe Fuel Cell

A

An electrical cell that is supplied with fuel and oxygen (or air) and uses energy from the reaction between them to produce electrical energy efficiently

27
Q

Describe how a hydrogen fuel cell works

A

Hydrogen is oxidised to release energy

The only bi-product is water

28
Q

What acid is used as an electrolyte in a hydrogen fuel cell?

A

Phosphoric Acid

29
Q

What is at the cathode in a hydrogen fuel cell?

A

Oxygen

30
Q

What is at the anode in a hydrogen fuel cell?

A

Hydrogen

31
Q

What is the reaction at the cathode in a hydrogen fuel cell? Give the equation?

A

2O2++4H++4e–>2H2O

32
Q

What is the reaction at the anode in a hydrogen fuel cell? Give the equation?

A

H2->2H++2e-

33
Q

What is the overall equation for the reaction in a hydrogen fuel cell?

A

2H2+O2->2H2O

34
Q

Advantages to Hydrogen Fuel Cells

A
  • Non pollutant
  • Less expensive than batteries
  • Store more energy than batteries
35
Q

Disadvantages to Hydrogen Fuel Cells

A
  • Needs a lot of space (gas)
  • It is explosive
  • Often made by other hydrocarbons

UK GCSE Chemistry (9 decks)

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