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Chemistry AS > Energetics > Flashcards

Energetics Flashcards

Brownlow

1
Q

What is enthalpy change?

A

The change in heat content at constant pressure.

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2
Q

Is the change in heat in an exothermic reaction negative or positive?

A

Negative.

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3
Q

Is the change in heat in an endothermic reaction negative or positive?

A

Positive.

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4
Q

What is enthalpy?

A

The measure of the heat content of a substance.

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5
Q

What is enthalpy change?

A

The heat change in a reaction at a constant pressure.

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6
Q

What are endothermic reactions?

A

Reactions that absorb energy from the surroundings.

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7
Q

Is the enthalpy change for an endothermic reaction positive or negative?

A

Positive.

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8
Q

Why is an endothermics enthalpy change positive?

A

The products are higher in energy than the reactants.

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9
Q

What are exothermic reactions?

A

Reactions that release energy to the surroundings.

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10
Q

Why is an exothermics enthalpy change negative?

A

The product is lower in energy than reactants.

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11
Q

Is the enthalpy change for an exothermic reaction negative or positive?

A

Negative.

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12
Q

What do you need to break a bond?

A

Absorb energy.

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13
Q

Is bond breaking an endothermic or exothermic process?

A

Endothermic.

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14
Q

Why is bond breaking an endothermic process?

A

Energy is absorbed so the enthalpy change is positive.

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15
Q

If a reaction requires more energy for bonds to be broken than formed is the reaction endothermic or exothermic?

A

Endothermic.

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16
Q

What do you need to form a bond?

A

Release energy.

17
Q

Is bond forming an exothermic or endothermic process?

A

An exothermic process and the enthalpy change is negative.

18
Q

If a reaction releases more energy breaking bonds than it absorbs to form bonds is it endothermic or exothermic?

A

Exothermic.

19
Q

What is the equation for enthalpy change?

A

Total energy to break bonds - total energy released forming bonds.

20
Q

What is calorimetry?

A

The method used to work out the enthalpy change of combustion.

21
Q

What is the first step of calorimetry for a fuel?

A

A fuel is burned to raise the temperature of the water by a specific amount. Generally we weigh the fuel before and after burning to work out the mass of fuel burned.

22
Q

What is the second step of calorimetry for a fuel?

A

The energy from the fuel is transferred into the water although some is lost to the surroundings too.

23
Q

Why is a lid placed on top in calorimetry for a fuel?

A

To prevent heat loss.

24
Q

Why are wind shields placed near the flame in calorimetry for a fuel?

A

To prevent a draught from moving the flame.

25
Q

What is the equation to calculate the energy transferred in calorimetry?

A

q = M * c * delta T

26
Q

What does q stand for in the equation to calculate the energy transferred in calorimetry?

A

Heat energy lost or gained.

27
Q

What does m stand for in the equation to calculate the energy transferred in calorimetry?

A

MAss of water or solution.

28
Q

What does c stand for in the equation to calculate the energy transferred in calorimetry?

A

Specific heat capacity of water.

29
Q

What does delta T stand for in the equation to calculate the energy transferred in calorimetry?

A

Temperature change.

30
Q

What unit is temperature measured in the equation used to calculate the energy transferred in calorimetry?

A

Kelvin.

31
Q

What unit is mass measured in the equation used to calculate the energy transferred in calorimetry?

A

Grams.

32
Q

What unit is heat or energy lost or gained measured in the equation used to calculate the energy transferred in calorimetry?

A

Joules.

33
Q

What is the specific heat capacity of water?

A

4.18 Jg^-1K^-1.

34
Q

What is the first step of calorimetry of a solution?

A

Add acid and mesure temperature.

35
Q

What is the second step of calorimetry of a solution?

A

Add alklai/solid and stir and measure temperature change.

36
Q

What does Hess’ law state?

A

The total enthalpy change of a reaction is independent of the route taken.

37
Q
A

Chemistry AS (16 decks)

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