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Chemistry Paper 1 > Topic 5 Energy Changes > Flashcards

Topic 5 Energy Changes Flashcards

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1
Q

What is an exothermic reaction?

A

Transfers energy to surroundings so temperature of surroundings increases

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2
Q

What are 3 examples of exothermic reactions?

A

Combustion
Neutralisation
Many oxidation reactions

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3
Q

What are 2 everyday uses of exothermic reactions?

A

Hand warmers
Self-heating cans

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4
Q

What is an endothermic reaction?

A

Takes in energy from surroundings so temperature of surroundings decreases

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5
Q

What are 2 examples of endothermic reactions?

A

Thermal decomposition
Reaction of citric acid and sodium hydrogencarbonate

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6
Q

What is an everyday use of an endothermic reaction?

A

Sports injury packs

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7
Q

What do reaction profiles show?

A

Relative energies of reactants and products, activation energy and overall energy change

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8
Q

What is the activation energy?

A

Minimum amount of energy that particles must have to react

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9
Q

When can chemical reactions only occur?

A

Reacting particles collide with each other with sufficient energy

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10
Q

How is an exothermic reaction represented on a reaction profile?

A

Products at lower energy level than reactants

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11
Q

How are endothermic reactions represented on a reaction profile?

A

Products at higher energy level than reactants

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12
Q

What does the initial rise in energy on a reaction profile represent?

A

Activation energy

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13
Q

What happens during a chemical reaction?

A

Old bonds broken and new bonds formed

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14
Q

What is needed to break bonds in the reactants?

A

Energy must be supplied

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15
Q

What type of process is bond breaking?

A

Endothermic

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16
Q

What happens when new bonds in the products are formed?

A

Energy released

17
Q

What type of process is bond formation?

A

Exothermic

18
Q

In an exothermic reaction, what is the energy released from forming new bonds greater than?

A

Energy needed to break existing bonds

19
Q

In an endothermic reaction, what is the energy needed to break bonds greater than?

A

Energy released from forming new bonds

20
Q

What can be calculated from bond energies?

A

Energy needed to break bonds and energy released when bonds are formed

21
Q

How can you calculate the overall energy change in a reaction?

A

Sum of energy needed to break bonds in reactants minus sum of energy released when new bonds formed in products

22
Q

How can a simple cell be made?

A

Connecting 2 different metals/electrodes in contact with electrolyte

23
Q

How is a cell set up?

A

Electrodes connected by wire, voltmeter connected

24
Q

What 2 things is the voltage produced by a cell dependent on?

A

Electrolyte
Type of electrode

25
Q

What does the electrolyte in a cell contain that reacts with the electrodes?

A

Ions

26
Q

What causes the pd of a cell?

A

Different metals react differently with same electrolyte

27
Q

What is the rule for pd of a cell?

A

Bigger difference in reactivity of electrodes, bigger voltage of cell

28
Q

What is a battery?

A

Two or more cells connected in series, provide greater voltage

29
Q

Why does a battery have a greater voltage?

A

Voltages of cells combined

30
Q

What is an example of non-rechargeable batteries?

A

Alkaline Batteries

31
Q

When does electricity stop being produced in non-rechargeable cells/batteries?

A

Reactants used up

32
Q

Why can rechargeable cells/batteries be recharged?

A

Reaction can be reversed by connecting an external electric current

33
Q

What are 2 types of electrical energy vehicles can use?

A

Batteries
Hydrogen-oxygen fuel cells

34
Q

What are 2 disadvantages of using batteries (compared to using fuel cells)?

A

Rechargeable batteries eventually need replacing
Batteries store less energy than fuel cells- need recharging more often

35
Q

What are 2 disadvantages of using hydrogen fuel cells (compared to batteries)?

A

Hydrogen is explosive (when mixed with air), hard to store safely
Hydrogen is gas- takes up more space to store

36
Q

What is a fuel cell supplied with?

A

Fuel and oxygen/air

37
Q

How is a pd produced in a fuel cell?

A

Fuel oxidised electrochemically within fuel cell

38
Q

What are hydrogen fuel cells a potential alternative to?

A

Rechargeable batteries/cells

39
Q

What is the overall reaction in a hydrogen fuel cell?

A

Hydrogen oxidised to produce water

Chemistry Paper 1 (6 decks)

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