Chapter 9- Enthalpy Flashcards Preview

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Flashcards in Chapter 9- Enthalpy Deck (20)
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1
Q

Define enthalpy

A

The heat content that is stored in a chemical system

2
Q

What is enthalpy stored in?

A

kJmol-1

3
Q

Define activation energy

A

The minimum energy required to start a reaction by the breaking of bonds

4
Q

Give 2 examples of endothermic reactions

A

Thermal decomposition

Photosynthesis

5
Q

Give 2 examples of exothermic reactions

A

Combustion

Neutralisation

6
Q

What happens in a exothermic reaction?

3 things

A

Enthalpy of the product is smaller than that of the reactants
There is heat loss FROM the SYSTEM TO the SURROUNDINGS
The enthalpy change has a NEGATIVE sign because heat is LOST from the chemical system

7
Q

What happens in an endothermic reaction?

3 things

A

Enthalpy of the product is larger than that of the reactants
There is a heat gain TO the SYSTEM FROM the SURROUNDINGS
The surroundings DECREASE in temperature
The enthalpy has a positive sigh because heat has been gained by the chemical system

8
Q

What 2 things do you need to write in an exam question to prove a reaction profile is endothermic?

A

The enthalpy of the reactants is LOWER than the enthalpy of the product

The enthalpy change is POSITIVE so energy is TAKEN IN FROM the surroundings

9
Q

What 2 things do you need to write in an exam question to prove a reaction profile is exothermic?

A

The enthalpy of the reactants is HIGHER than the enthalpy of the product

The enthalpy change is NEGATIVE so energy is GIVEN OUT TO the surroundings

10
Q

Is energy taken in to break bonds or make bonds?

A

To break bonds

11
Q

Is energy given out to break bonds or make bonds?

A

Make bonds

12
Q

Explain the relationship between exothermic energy profiles and bonds

A

More energy ie released when bonds are made than when bonds are broken

13
Q

Explain the relationship between endothermic energy profiles and bonds

A

Less energy is release when bonds are made than is taken in than when bonds are broken

14
Q

What are the standard conditions in enthalpy changes?

A

100kPa
298K
1moldm-3 for a solution reaction

15
Q

What are standard states?

A

The physical state of a substance being under the standard conditions of 100kPa and 298K

16
Q

What is 🔼H?

A

The enthalpy changes under standard conditions

17
Q

Define standard enthalpy changes of reactions

A

The enthalpy change that accompanies a reaction in the molar quantities expressed in the chemical equation in their standard states under their standard conditions of 100kPa and 298K

18
Q

Define standard enthalpy changes of combustion

A

The enthalpy change that takes place when 1 mole of a substance reacts completely with oxygen in their standard states under the standard conditions of 100kPa and 298K

19
Q

Define standard enthalpy changes of neutralisation

A

The enthalpy change that accompanies the reaction of an acid and an alkali or base to form 1 mole of H20 in their standard states and under the standard conditions of 100kPa and 298K

20
Q

Define standard enthalpy changes of formation

A

The enthalpy change that takes plafe when 1 mole of a compound is formed from its constituent elements in their standard states under the standard conditions of 100kPa and 298 K