Unit 5- Energy Changes and reversible reactions Flashcards

1
Q

State the law of conservation of energy.

A

Energy cannot be created or destroyed, it can only transferred from one place to another.

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2
Q

How does the law of conservation of energy apply to chemistry?

A

In all chemical reactions, energy is either transferred to the surroundings or from the surroundings.

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3
Q

What is an exothermic reaction?

A

A reaction where energy is transferred to the surroundings.

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4
Q

Give two examples of exothermic reactions.

A

Combustion, respiration

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5
Q

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

A

They increase. The thermometer is included in “the surroundings” so shows the temperature increasing.

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6
Q

What is an endothermic reaction?

A

A reaction where energy is transferred from the surroundings.

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7
Q

Give two examples of endothermic reactions.

A

Thermal decomposition reactions, citric acid and sodium hydrogencarbonate.

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8
Q

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

A

They decrease. The thermometer is included in “the surroundings” so shows the temperature decreasing.

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9
Q

State two uses of exothermic reactions

A

Self-heating cans, hand warmers

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10
Q

State two uses of endothermic reactions

A

Some cooling sports injury packs

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11
Q

What are reactants?

A

The substances involved in a chemical reaction

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12
Q

What are products?

A

The substances formed when reactants have a chemical reaction

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13
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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14
Q

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

A

An exothermic one. The missing energy has been transferred to the surroundings.

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15
Q

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

A

An endothermic one. The extra energy has been take in by the surroundings.

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16
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)

17
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)

18
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.

19
Q

What is a reversible reaction?

A

A reaction which can go from reactants to products but also from products to reactants

20
Q

What chemical symbol represents a reversible reaction?

A

21
Q

If a reaction is exothermic in the forward direction what will it be in the reverse direction?

A

Endothermic

22
Q

Two reactants require 30kJ to turn into products. What energy transfer is involved when the products turn into reactants?

A

30kJ is released

23
Q

What is equilibrium?

A

The point in a reversible reaction when the forward and reverse reactions are occurring at the same rate

24
Q

How is the amount of reactant changing at equilibrium?

A

The point in a reversible reaction when the forward and reverse reactions are occurring at the same rate

25
Q

What is Le Chatelier’s principle?

A

When a reaction at equilibrium is changed, it will seek to counteract that change

26
Q

How is the amount of reactant changing at equilibrium?

A

It is not changing

27
Q

How is the amount of product changing at equilibrium?

A

It is not changing

28
Q

A reaction is exothermic in the forward direction. What will occur if the temperature is increased?

A

The backward reaction will increase as it is endothermic and will reduce the temperature

29
Q

A reaction is at equilibrium when some product is removed. What will occur?

A

The forward reaction will increase as that will increase the amount of product

30
Q

The reaction below is at equilibrium. What will occur when the pressure is increased? 2H₂(g) + O₂(g) ⇌ 2H₂O(g)

A

The forward reaction will increase as there are fewer molecules on the right. This will reduce the total number of molecules and therefore the pressure.