Enthalpies

Question 1

What is the Law of Conservation of Energy?

Answer 1

That energy can never be destroyed or created, but only transfered from one store to another…

Question 2

What is Enthalpy?

Answer 2

The measure of Thermal Energy involved in a chemical reaction

Question 3

How can we find the Enthalpy Change?

Answer 3

H(products) - H(reactants) = delta H

delta H will be positive when products having more energy than reactants….

and opposite goes the same……….

Question 4

What happens during exothermic and endothermic reactions?

Answer 4

1. EXO = Energy transfered from the sytem to surroundings, with TEMP INCREASE
2. ENDO = Energy transfered to sytem from system to surroundings, with TEMP DECREASE.

Question 5

What are the Standard Enthalpy Conditions?

Answer 5

1. Pressure = 100 Kpa (1 atm)
2. Temperature = 25.C (298K)
3. Concentration = 1moldm-3
4. Physical State = its state at RTP

Question 6

What is the Standard Enthalpy Change of Reactions?

Answer 6

• Enthalpy change that accompanies a reaction in molar quantities shown in chemical equations, under standard conditions!

Question 7

What is the Standard Enthalpy Change of Formation?

Answer 7

• Enthalpy change taking place when one mole of a compound is formed from its own elememts, under standar conditions

Question 8

What is the Standard Enthalpy Change of Combustion?

Answer 8

• Enthaply change taking place when 1 mole of a compound is completely burned with oxygen, under standard conditions

Question 9

What is the Standard Enthalpy Change of Neutralisation?

Answer 9

• Enthalpy change that accompanies a neutralisation reaction, with a base and an acid, to form 1 mole of liquid water, under standard conditions!

Question 10

What is Hess’ Law?

Answer 10

“If a reaction can occur in **2 or multiple routes **with the exact same initial and final conditions, the enthalpy chamge will remain the same for all routes!!

Question 11

How can we construct enthalpy change for formation?

Answer 11

• Using arrow POINTING UP, labelling delta H 1,2 and 3 in correspondong directions
• Using Route 1 and Route 2 rule equations to find enthalpy changes

ROUTE 2 = -delta H2 +delta H3

Question 12

How can we construct enthalpy change for combustion?

Answer 12

• Using arrow POINTING DOWN, labelling delta H 1,2 and 3 in correspondong directions
• Using Route 1 and Route 2 rule equations to find enthalpy changes

ROUTE 2 = delta H2 - delta H3