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Chemistry > Unit 5 energy changes > Flashcards

Unit 5 energy changes Flashcards

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1
Q

What is an exothermic reaction?

A

A reaction where energy is transferred to the surroundings.

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2
Q

Give examples of exothermic reactions.

A

Combustion, respiration and many neutralisation reactions

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3
Q

What happens to the temperature of the surroundings during an exothermic reaction?

A

They increase

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4
Q

What is an endothermic reaction?

A

A reaction where energy is transferred from the surroundings.

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5
Q

Give examples of endothermic reactions.

A

Thermal decomposition reactions, the reaction between citric acid and sodium hydrogencarbonate and respiration

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6
Q

What happens to the temperature of the surroundings during an endothermic reaction?

A

They decrease

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7
Q

State two uses of exothermic reactions

A

Self-heating cans, hand warmers

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8
Q

State two uses of endothermic reactions

A

Some cooling sports injury packs

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9
Q

What are reactants?

A

The substances involved in a chemical reaction

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10
Q

What are products?

A

The substances formed when reactants have a chemical reaction

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11
Q

What is a reaction profile?

A

A diagram which shows whether the reactants have more or less energy than the products.

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12
Q

Why does the reaction profile always go up at the start?

A

A reaction starts with bonds being broken

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13
Q

What is the activation energy?

A

The energy needed to break bonds to start a reaction

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14
Q

Why does the reaction profile always go down at the end?

A

A reaction always ends with bonds being made

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15
Q

If the reactants have more energy than the products, what kind of a reaction must have taken place?

A

An exothermic one. Energy has been transferred to the surroundings.

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16
Q

If the reactants have less energy than the products, what kind of reaction must have taken place?

A

An endothermic one. Energy has been taken in from the surroundings.

17
Q

Is breaking bonds endothermic or exothermic?

A

Endothermic.
Chemical bonds are strong so require energy to break (like when you have to put energy in to separate magnets from each other)

18
Q

Is making bonds endothermic or exothermic?

A

Exothermic.
Energy is released when chemical bonds are formed (like how two magnets move together when close and generate kinetic energy)

19
Q

How do we work out the overall energy change of a reaction?

A

Work out the difference between the energy needed to break all the bonds in the reactants and the energy released to form all the bonds in the products.

20
Q

How do we work out the energy change from a reaction profile?

A

The difference between the energy of the reactants and the energy of the products

21
Q

How do we work out the activation energy from a reaction profile?

A

The difference between the energy of the reactants and the highest point on the profile

22
Q

What is a chemical cell?

A

A unit which contains chemicals which produce electricity through a reaction

23
Q

What are the main components of a chemical cell?

A

An anode, a cathode (made of 2 different metals) and an electrolyte

24
Q

What is an electrolyte?

A

A solution containing ions

25
Q

What does the voltage of a cell depend on?

A

The type of electrode and the electrolyte.

26
Q

What is a battery?

A

Two or more cells connected in series

27
Q

What happens to the electrodes in a chemical cell?

A

The more reactive metal is used up and the less reactive one increases in size.

28
Q

In non-rechargeable cells, why do the chemical reactions stop over time?

A

One of the reactants becomes used up.

29
Q

How can certain cells be recharged?

A

Applying an external electric current

30
Q

How does the reactivity of the metal electrodes affect the size of the potential difference?

A

The greater the difference in reactivity, the greater the voltage

31
Q

Which way do electrons move in a cell?

A

From the more reactive metal to the less reactive metal

32
Q

What is a fuel cell?

A

A cell which uses a fuel and oxygen (or air) to generate electricity.

33
Q

What are the products in a hydrogen fuel cell?

A

Water

34
Q

State advantages of hydrogen fuel cells

A

Do not need to be recharged, no pollutants are produced

35
Q

State three disadvantages of hydrogen fuel cells

A

Hydrogen is highly flammable, hydrogen is often made from fossil fuels, hydrogen is difficult to store

36
Q

What reaction occurs at the negative electrode of a hydrogen fuel cell

A

H2 → 2H + 2e⁻

37
Q

Which reaction occurs at the positive electrode of a hydrogen fuel cel

A

O2 + 4H+ + 4e- → 2H2

Chemistry (5 decks)

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