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GCSE Chemistry > Energy Changes > Flashcards

Energy Changes Flashcards

1
Q

What is an exothermic reaction?

A

Energy is transferred to the surroundings (exits)

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2
Q

What happens to the temperature of an
exothermic reaction?

A

Temperature increases

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3
Q

What is an endothermic reaction?

A

Energy is taken in from the surroundings

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4
Q

What happens to the temperature of an
endothermic reaction?

A

Temperature decreases

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5
Q

Give examples of exothermic reactions

A

Combustion
Neutralisation
Respiration
Oxidation reactions

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6
Q

Give every day uses of exothermic
reactions

A

Self-heating cans
Hand warmers

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7
Q

Give examples of endothermic reactions

A

Thermal decomposition
Photosynthesis
Citric acid and sodium hydrogen carbonate (sherbet)

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8
Q

Give every day uses of endothermic
reactions

A

Sports injury packs

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9
Q

What is the energy of the products
compared to reactants in an exothermic
reaction?

A

Less

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10
Q

What is the energy of the products
compered to reactants in an endothermic
reaction?

A

More

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11
Q

What is activation energy ?

A

Minimum energy that particles must have for a reaction
to occur

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12
Q

What does a reaction profile show?

A

It is a graphical representation of energy vs reaction progression.

It allows us to see how the energy of the reactants and products change over a reaction.

It should always include the activation energy (represented as a hump going from the reactants).

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13
Q

Draw a reaction profile for an exothermic
reaction

A
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14
Q

Draw a reaction profile for an endothermic
reaction

A
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15
Q

What does a catalyst do to the activation
energy

A

Lowers it, by providing an alternative path

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16
Q

Draw a reaction profile for a reaction with
a catalyst

A
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17
Q

What is needed to break a bond

A

Energy

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18
Q

REQUIRED PRACTICAL: How can you
investigate variables that affect temperature changes in reacting solutions such as:
Acid + metal
Acid + metal carbonate
Acid + base
Displacement reactions
Note this method is very generic as depends what the independent/ dependent variables are.

A
  1. Use an insulating beaker, add an appropriate volume
    of liquid using a measuring cylinder.
  2. Measure the initial temperature and record this.
  3. Add a set mass (e.g. 1g) of the other reactant and
    stir
  4. Measure the highest temperature or measure the
    temperature after a set time and record this.
  5. Calculate the temperature difference
  6. Repeat with same volume of liquid but different
    masses or different reactants (depends what
    investigating)
19
Q

What type of process is bond breaking

A

Endothermic

20
Q

What is given out when a bond is made

A

Energy

21
Q

What type of process is bond making

A

Exothermic

22
Q

Why is a reaction endothermic overall in
terms of bonds breaking and making

A

More energy is taken in during bond breaking than is
given out during bond making

23
Q

Why is a reaction exothermic overall in
terms of bonds breaking and making

A

More energy is given out during bond making than is
taken in during bond breaking

24
Q

How can you calculate the overall energy
change in a reaction

A

Sum of bonds broken - sum of bonds made
AKA (reactants – products)

25
Q

Here is an example calculation

A
26
Q

What do cells contain

A

Chemicals which react to produce electricity

27
Q

What is the voltage of a cell dependent on

A

Type of electrode (different metals)
Electrolyte
Concentration of electrolyte
Temperature

28
Q

How can a simple cell be made

A

Connecting two different metals (have different reactivity)
Putting these in contact with an electrolyte.

The bigger the difference in reactivity between the two metals the larger the voltage.

29
Q

What is an electrolyte

A

A liquid that contains ions which react with the electrode

30
Q

How does the voltage produced in a cell represent the reactivity of the metals?

A

Larger the positive voltage, the more reactive the
metal

31
Q

What is a battery

A

Two or more cells connected together in series to provide a greater voltage.

E.g. connect two 1.5V cells in series to produce a 3.0V battery.

32
Q

What are non-rechargeable cells and
batteries

A

The chemical reaction is irreversible
Stops when one of the reactants have been used up
Alkaline batteries are non-rechargeable

33
Q

What are rechargeable cells and
batteries

A

Chemical reactions are reversible
When an external electrical circuit is supplied

34
Q

What is a fuel cell

A

Supplied by an external source of fuel (e.g.Hydrogen and Oxygen/air)

The fuel is oxidised electrochemically within the fuel cell to produce a potential difference.

35
Q

How are fuel cells and chemical cells
different?

A

Fuel cells produce a voltage continusouly as long as they have:
A supply of a suitable fuel Oxygen

Fuel cells oxidise the fuel electrochemically (in
chemical cells the fuel is burned)

36
Q

What is a common fuel used in a fuel
cell

A

Hydrogen

37
Q

What solutions can be used as the
electrolyte in a hydrogen fuel cell

A

An alkali e.g. potassium hydroxide
An acid e.g. hydrochloric acid

38
Q

If the electrolyte is an alkali
What happens at the negative electrode (anode)?
Write a half equation to represent this.

A

Hydrogen reacts with hydroxide ions to produce water.
This produces electrons
H2 + 2OH- → 2e- + 2H2O

39
Q

If the electrolyte is an alkali
What happens at the positive electrode
(Anode)?

A

Oxygen reacts with water to produce hydroxide ions.
This uses up the electrons (produced from anode).

O2 + 4e- + 2H2O → 4OH-

40
Q

If the electrolyte is an acid
What happens at the positive electrode
(cathode)?

A

Oxygen is reduced (gains electrons)
O2 + 4H+ + 4e-→ 2H2O

41
Q

If the electrolyte is an acid
What happens at the negative
electrode (cathode)?
Write a half equation to represent this.

A

H2 → 2H+ + 2e-

Hydrogen is oxidised (loses electrons)

42
Q

What is the overall equation for the
hydrogen-fuel cell?

A

2H2 + O2 → 2H2O
Hydrogen + oxygen → water
(In the alklai: the 4OHions, 4e- and 2H2O molecules
cancel out)

43
Q

Name advantages for a hydrogen fuel
cell

A
  • Coventional fuels are finite so saves resources,
  • Does not produce pollutants (no CO2 produced)
  • Only by products are water and heat
  • Faster to refuel (than recharging)
  • Can travel further
  • Can be renewable if hydrogen is made by electrolysis using renewable energy
44
Q

Name disadvantages for a hydrogen fuel
cell

A
  • Hydrogen is made from fossil fuels
  • Difficult to store
  • Hydrogen is made from non-renewable resources
  • Hydrogen is explosive so safety issues
  • Costs more to refuel (than recharging)
  • Costs more to manufacture
  • Not many hydrogen filling stations

GCSE Chemistry (8 decks)

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