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GCSE Chemistry LTS > Chapter 7 Energy Changes > Flashcards

Chapter 7 Energy Changes Flashcards

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1
Q

Why do chemical reactions occur?

A

Chemical reactions occur so that elements can achieve a more stable energy state by gaining a full outer shell of electrons.

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2
Q

How can a more stable energy state be achieved?

A

A more stable energy state is achieved through chemical bonding. This involves making and breaking chemical bonds (like covalent and ionic bonds).

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3
Q

What does the making and breaking of bonds involve?

A

The making and breaking of bonds involves the transfer of energy.

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4
Q

What form is the transferred energy usually in?

A

Usually the energy transferred is in the form of heat.

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5
Q

What is thermodynamics?

A

Thermodynamics literally means heat and movement and is the branch of physical chemistry that deals with heat, energy, temperature and the physical properties of matter.

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6
Q

What is the Law of Conservation of Energy?

A

When a chemical reaction occurs, energy (E) is conserved – the amount of energy before the reaction is equal to the amount of energy after the reaction.

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7
Q

When looking at thermodynamics, what is the system and what are the surroundings?

A

The system is what is happening in the chemical reaction. The surroundings are outside the chemical reactions.

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8
Q

What type of reaction involves a net release of energy?

A

Exothermic reaction.

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9
Q

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

A

The temperature of the surroundings increases.

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10
Q

Give 3 examples of exothermic reactions.

A

Examples of types of exothermic reactions include:
1. Combustion

  1. Oxidation
  2. Neutralisation
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11
Q

Give 2 uses of exothermic reactions in commercial products.

A

Handwarmers.

Self heating cans of food and drinks.

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12
Q

What type of reaction involves energy being taken in from the surroundings?

A

Endothermic reaction.

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13
Q

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

A

The temperature of the surroundings decreases.

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14
Q

Which are more common, exothermic or endothermic reactions?

A

Exothermic reactions are more common.

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15
Q

Give 4 examples of typical endothermic reactions.

A

Examples of endothermic reactions include:
1. Electrolysis

  1. Thermal decomposition reactions
  2. The first stages of photosynthesis
  3. The reaction between citric acid and sodium hydrogencarbonate.
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16
Q

Give an example of a commercial product that uses an endothermic reaction.

A

Cold packs.

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17
Q

How do we measure changes in heat in chemical experiments?

A

We can use a thermometer.

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18
Q

What happens to the overall energy in a chemical reaction?

A

Overall energy is conserved. It is transferred but it isn’t created or destroyed.

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19
Q

If heat energy is transferred to the surroundings what will happen to the temperature of the reaction.

A

The temperature will increase.

20
Q

In an exothermic reaction will the products have more or less energy than the reactants?

A

The products will have less energy than the reactants because some of the energy from the reactants has been transferred to heat energy and released to the surroundings.

21
Q

What is a reaction profile?

A

A reaction profile is a diagram showing the energy in a chemical reaction.

22
Q

What is activation energy?

A

Activation energy is the minimum energy required for a collision between reactants to be successful and result in products forming. It is required to break the bonds in the reactants.

23
Q

How is activation energy represented in a reaction profile?

A

There will always be an increase in potential energy at the start of the reaction. This is the activation energy.

24
Q

Draw the reaction profile for an exothermic reaction.

A
25
Q

In an endothermic reaction will the products have more or less energy than the reactants?

A

The products will have more energy than the reactants because energy is taken in from the surroundings during the reactions and is used to create the products.

26
Q

Draw the reaction profile for an endothermic reaction.

A
27
Q

Does breaking bonds require energy or release energy?

A

Breaking bonds aBsorbs (requires) energy. It is endothermic.

28
Q

Does forming bonds require energy or release energy?

A

FoRming bonds releases energy. It is exothermic.

29
Q

Describe in detail how energy changes in a chemical reaction can be investigated.
This is a required practical.

A
  1. Use a polystyrene cup as your reaction vessel. This is important because polystyrene acts as an insulator reducing the movement of heat.
  2. Use a thermometer to take and record the initial temperatures of the 2 reactants.
  3. Mix your reactants in the polystyrene cup and record the highest (or lowest) temperature reached.
  4. Calculate the temperature change.
  5. Draw a reaction profile for the reaction.
30
Q

If the concentration of one of the reactants is increased in the investigation why does the increase in temperature eventually start to decrease?

A

Eventually one of the reactants becomes limiting so no further reaction takes place. Heat then starts to be lost to the surroundings resulting in a decrease in temperature.

31
Q

What is bond energy?
(HIGHER ONLY)

A

Bond energy is the energy needed to break the bond between 2 atoms.

32
Q

What units are used to measure bond energy?
(HIGHER ONLY)

A

Bond energy is measured in kJ/mol.

33
Q

Describe how to calculate the energy change for a reaction.
(HIGHER ONLY)

A
  1. Write the chemical equation for the reaction.
  2. Balance the chemical equation.
  3. Draw out all the structural formulae for all reactants in the chemical reaction to include bonds.
  4. Identify how many of each bond there are. Be sure to take into account how many molecules there are in the balanced equation.
  5. Use the bond energies provided to calculate the total energy in bonds broken from the reactants..
  6. Use the bond energies to calculate the total energy in the fonds formed.
  7. Subtract the energy in bonds formed from the energy in bonds broken.
  8. If the result is negative the reaction is exothermic. If the result is positive the reaction is endothermic.
34
Q

What are simple cells used for?
(TRIPLE ONLY)

A

A source of electrical energy.

35
Q

How could we make a simple electrical cell?
(TRIPLE ONLY)

A

Place 2 electrodes made of different metals into an electrolyte. This is how ‘lemon’ cells work.

36
Q

Why does the lemon cell made with copper and zinc produce electricity?
(TRIPLE ONLY)

A

Zinc is more reactive than copper so will release electrons. This makes the Zinc positively charged. These electrons flow around the circuit to the copper.

37
Q

How can the voltage produced between the 2 electrodes be increased?
(TRIPLE ONLY)

A

The voltage can be increased by choosing metals that are further apart in the reactivity series. The greater the difference in the reactivity the greater the voltage produced.

38
Q

What else can affect the voltage produced?
(TRIPLE ONLY)

A

The electrolyte used can have an impact on the voltage produced.

39
Q

What is a battery?
(TRIPLE ONLY)

A

A battery is 2 or more cells connected in series.

40
Q

Why do batteries go flat?
(TRIPLE ONLY)

A

Once one of the reactants is used up no more voltage will be produced. The reaction is irreversible so the battery must be replaced.

41
Q

Why can some batteries be recharged?
(TRIPLE ONLY)

A

Rechargeable batteries use reversible reactions that can be reversed through applying an electrical charge.

42
Q

Why should batteries not be put in the household waste?
(TRIPLE ONLY)

A

Batteries are toxic and corrosive. They can also cause fires in landfill sites.

43
Q

What is a fuel cell?
(TRIPLE ONLY)

A

A fuel cell is an electrochemical cell in which a fuel donates electrons at one electrode and oxygen gains electrons at the other electrode.

44
Q

Describe how a fuel cell works.
(TRIPLE ONLY)

A

Fuel enters the cell.

The fuel is oxidised (loses electrons). This sets up a potential difference or voltage within the cell.

Electrons flow to the other electrode generating electricity.

45
Q

What is a hydrogen-oxygen fuel cell?
(TRIPLE ONLY)

A

A hydrogen-oxygen fuel cell is an example of a fuel cell that combines oxygen and hydrogen to release energy and water.

46
Q

Why are fuel cells important?
(TRIPLE ONLY)

A

We need to reduce our reliance on fossil fuels for vehicles. Fuel cells are a carbon free source of energy.

GCSE Chemistry LTS (15 decks)

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