Energy Change (C5) Flashcards

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
How do rechargable batteries work?
The reaction is reversible so when hooked up to an external electric current it is reversed and the reactants can be re-used
26
Describe Fuel Cell
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
Describe how a hydrogen fuel cell works
Hydrogen is oxidised to release energy | The only bi-product is water
28
What acid is used as an electrolyte in a hydrogen fuel cell?
Phosphoric Acid
29
What is at the cathode in a hydrogen fuel cell?
Oxygen
30
What is at the anode in a hydrogen fuel cell?
Hydrogen
31
What is the reaction at the cathode in a hydrogen fuel cell? Give the equation?
2O2++4H++4e-->2H2O
32
What is the reaction at the anode in a hydrogen fuel cell? Give the equation?
H2->2H++2e-
33
What is the overall equation for the reaction in a hydrogen fuel cell?
2H2+O2->2H2O
34
Advantages to Hydrogen Fuel Cells
- Non pollutant - Less expensive than batteries - Store more energy than batteries
35
Disadvantages to Hydrogen Fuel Cells
- Needs a lot of space (gas) - It is explosive - Often made by other hydrocarbons