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Energy Changes (seneca) Flashcards

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1
Q

in endothermic reactions, energy from the —— is transferred to the ——-, causing the temperature of the surroundings to …

A

surroundings
reacting chemicals
decrease

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2
Q

what are some examples of endothermic reactions

A

-thermal decomposition
- The melting of ice to form water.
-Evaporation of liquid water, forming water vapour.
-The baking of bread.
-sports injury packs
-Citric acid + baking soda

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3
Q

in exothermic reactions, energy from the——– is transferred to the ———-, which often —— the temperature as a result

A

reacting chemicals
surroundings
increases

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4
Q

what are examples of exothermic reactions

A

Combustion.
Neutralisation.
Oxidation.
handwarmers

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5
Q

Particles of the reactants have to …

A

collide.

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6
Q

The collisions that happen between particles of the reactants must take place with ———.
This threshold amount of energy is called the…

A

enough energy.
activation energy.

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7
Q

Reaction profiles show the 1. on the x-axis and 2. on the y-axis.

A

1.progress of reaction
2.energy level

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8
Q

Reaction profiles tell us:

A

-The amount of energy contained within the reactants and the products.
-The activation energy of a reaction.
-The overall energy change that happens as a result of a reaction.

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9
Q

What information is contained within reaction profile diagrams?

A

-The amount of energy contained within the reactants and the products
-The activation energy
-Overall energy change

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10
Q

Catalysts can 1 reaction rates by 2, which …

A

1.increase
2.lowering the activation energy
3.increases the likelihood of successful collisions.

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11
Q

collisions must have

A

sufficient energy

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12
Q

in endothermic reactions, Energy released by making bonds – energy required to break bonds

A

<

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13
Q

in endothermic reactions, overall energy change of reaction >

A

0

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14
Q

in exothermic reactions, Energy released by making bonds – energy required to break bonds.

A

>

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15
Q

in exothermic reactions, overall energy change of reaction <

A

0

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16
Q

Bond making releases 1. It is an 2 process.

A

1.heat energy
2.exothermic

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17
Q

Bond breaking needs 1. It is an 2. process.

A
  1. heat energy
    2.endothermic
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18
Q

A reaction is endothermic if…

A

the total energy released by forming bonds is less than total energy required to break bonds.

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19
Q

what is a catalyst?

A

A substance that increases the reaction rate by decreasing activation energy

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20
Q

By subtracting the 1. from the 2. , we can see if a reaction is endothermic or exothermic.

A

1.total bond energies of products
2.total bond energies of reactants

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21
Q

A reaction is exothermic if …

A

the total energy released by forming bonds is more than total energy required to break bonds.

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22
Q

Batteries and cells contain …

A

chemicals that react to produce electricity.

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23
Q

We can make a simple cell by …

A

connecting 2 different electrodes and putting them in a liquid electrolyte.

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24
Q

In a chemical cell, the difference in the reactivity of the metals produces …

A

a voltage (electricity).

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25
Q

A chemical cell produces ——- until …

A

a potential difference
the reactants are used up.

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26
Q

How would you describe a cell made by connecting 2 different electrodes and submerging them in an electrolyte?

A

simple cell

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27
Q

The voltage output of a cell can be changed by …

A

changing the type of electrode, the type of electrolyte or both the type of electrode and the type of electrolyte.

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28
Q

Changing the electrolyte changes——-. This will result in the…

A
  • the reactions that happen at the electrodes
  • voltage output of the cell changing.
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29
Q

A 1. difference in reactivity between 2. will result in the 3…

A

1.greater
2.the two electrodes
3.cell having a greater voltage.

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30
Q

how would you change voltage output of a (chemical) cell

A

Type of electrode
Type of electrolyte

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31
Q

In a chemical cell, decreasing the difference in reactivity between the 2 electrodes will ——- the voltage output

A

decrease

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32
Q

In a chemical cell, electrodes must 1, so 2.

A

1.conduct electricity
2.metals are often chosen

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33
Q

In a chemical cell, electrolyte contains …

A

the ions that react with the electrodes.

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34
Q

Chemical cells contain chemicals that react to produce …

A

electricity

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35
Q

A battery is a collection of …

A

more than one cell joined in series (end-to-end).

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36
Q

The voltage of a battery is calculated as …

A

the sum of the voltages of its individual cell components.

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37
Q

When the chemicals in a battery run out, …

A

the battery can not be used anymore.

38
Q

voltage of a battery=

A

Σ(sum of) voltages of individual cell components

39
Q

Cells and batteries can be either …

A

rechargeable or non-rechargeable.

40
Q

In non-rechargeable cells and batteries (e.g. 1.), 2. reactions take place at the …

A

1.alkaline batteries
2.irreversible
3.electrodes

41
Q

In non-rechargeable cells and batteries, electricity can no longer be produced …

A

as soon as one of the reacting chemicals has run out.

42
Q

In rechargeable cells and batteries, connection to an electric current …

A

reverses the reactions that happen at the electrodes

43
Q

In rechargeable cells and batteries, electricity can continue to be produced as long as …

A

there is access to this external electric current.

44
Q

What category do alkaline batteries come under?

A

non-rechargeable

45
Q

what types of battery?
Connection to an electric current reverses the reactions that happen at the electrodes. This means that electricity can continue to be produced.

A

Rechargeable

46
Q

what types of battery?
Irreversible reactions take place at the electrodes. This means that electricity can no longer be produced as soon as one of the reacting chemicals has run out.

A

Non-rechargeable

47
Q

In a battery, if more cells are added in series (joined end-to-end), the voltage output of the battery will …

A

increase

48
Q

reactions at electrodes are

A

irreversible

49
Q

Fuel cells produce 1. using a reaction between 2. and 3

A
  1. electrical energy
  2. an external fuel source (often hydrogen)
  3. oxygen
50
Q

The fuel is added to the cell and then there is a…

A

constant supply of oxygen

51
Q

In fuel cells, The fuel is ——- and this creates a voltage.

A

oxidised

52
Q

In fuel cells, The fuel is oxidised and this creates a …

A

voltage

53
Q

what are the advantages of fuel cells ?

A

-Compact and lightweight
-Reliable
-Less pollution than traditional methods
-High efficiency

54
Q

why are fuel cells reliable?

A

The absence of moving parts means they are reliable.

55
Q

Fuels cells produce electrical energy efficiently by…

A

using energy produced by a particular reaction

56
Q

In hydrogen fuel cells, the ——–
of hydrogen generates a voltage and the only waste product is water.

A

oxidation

57
Q

In hydrogen fuel cells, the oxidation of hydrogen generates …

A

a voltage and the only waste product is water.

58
Q

what is the Hydrogen Fuel Cell anode half equation?

A

2H2 → 4H+ + 4e-

59
Q

what is the Hydrogen Fuel Cell cathode half-equation ?

A

O2 + 4H+ + 4e- → 2H2O

60
Q

what is the Hydrogen Fuel Cell cathode overall equation ?

A

2H2 + O2 → 2H2O

61
Q

ANODE HALF EQUATION -Hydrogen is pumped in at the —–. Hydrogen ions are formed as hydrogen molecules are oxidised and lose electrons.

A

anode

62
Q

ANODE HALF EQUATION -Hydrogen is pumped in at the anode. Hydrogen ions are formed as …

A

hydrogen molecules are oxidised and lose electrons.

63
Q

ANODE HALF EQUATION -Hydrogen is pumped in at the anode. ——– are formed as hydrogen molecules are oxidised and lose electrons.

A

Hydrogen ions

64
Q

CATHODE HALF EQUATION- Oxygen is pumped in at the ——. Water is formed as the O2 reacts with the H+ ions that have moved through the electrolyte from the anode.

A

cathode

65
Q

CATHODE HALF EQUATION- —— is pumped in at the cathode. Water is formed as the O2 reacts with the H+ ions that have moved through the electrolyte from the anode.

A

Oxygen

66
Q

CATHODE HALF EQUATION- Oxygen is pumped in at the cathode. Water is formed as the 1. reacts with the 2. that have moved through the electrolyte from the anode.

A

1.O2
2.H+ ions

67
Q

CATHODE HALF EQUATION- Oxygen is pumped in at the cathode. ——- is formed as the O2 reacts with the H+ ions that have moved through the electrolyte from the anode.

A

Water

68
Q

CATHODE HALF EQUATION - Oxygen is pumped in at the cathode. Water is formed as the O2 reacts with the H+ ions that have moved through …

A

the electrolyte from the anode.

69
Q

Which reactant is added to which electrode in hydrogen fuel cells?

A

-Oxygen is added to the cathode
-Hydrogen is added to the anode

70
Q

Hydrogen fuel cells can be used as alternatives to …

A

rechargeable batteries (and cells).

71
Q

hydrogen fuel cells may be better than rechargeable batteries and cells because:

A

-Toxicity
-Lifetime
-Capacity

72
Q

What are the risks of hydrogen fuel cells?

A

Hydrogen has to be stored at a high pressure and hydrogen gas is explosive.

73
Q

Batteries are made from …

A

toxic metal compounds and their disposal can cause pollution.

74
Q

Hydrogen fuel cells use ———– and the only waste product is …

A

hydrogen and oxygen
water

75
Q

Batteries must be replaced after …

A

a certain number of recharges.

76
Q

Hydrogen fuel cells can be reused indefinitely by …

A

adding more hydrogen and oxygen.

77
Q

Hydrogen fuel cells produce more energy per gram of…

A

hydrogen relative to petrol.

78
Q

Batteries have a —— capacity than hydrogen fuel cells, and so …

A

smaller
have to be charged more regularly.

79
Q

what are the advantages of hydrogen fuel cells?

A

-high capacity
-low toxicity
-long lifetime

80
Q

What is formed at the cathode in a hydrogen fuel cell?

A

water

81
Q

What are the reactants in fuel cells?

A

-An external fuel source
-Oxygen

82
Q

What is represented by the arrow going upwards in the reaction profile?

A

Activation energy

83
Q

in a reaction profile the shows to ‘leaps’ which ‘leap’ in the catalysed reaction?

A

the smaller ‘leap’

84
Q

How does a catalyst speed up the rate of reaction?

A

by lowering the activation energy

85
Q

Endothermic reactions —– energy from the surroundings

A

absorb

86
Q

Exothermic reactions —– energy into the surroundings

A

release

87
Q

The change in temperature =

A

final temperature - initial temperature

88
Q

Energy change (J) =

A

Volume of solution (cm3) x 4.2 x Change in temperature (C)

89
Q

Activation energy is the minimum amount of energy needed for particles to…

A

react.

90
Q

What does the bottom arrow represent in reaction graphs?

A

energy change

91
Q

what would be a suitable solution to act as a electrolyte

A

All soluble ionic compounds are strong electrolytes
Some polar covalent compounds are also strong electrolytes

92
Q

What’s the ionic equation that represents the reaction happening at the chromium electrode in the cathode cell?

A

Cr → Cr3+ + 3e−

science chemistry (18 decks)

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