Module 5- Hess' Law Defintions

Question 1

Standard enthalpy of combustion definition

Answer 1

The enthalpy change when 1 mol of substance is burnt completely in an excess of oxygen under standard conditions

Question 2

Standard enthalpy change of neutralisation

Answer 2

The enthalpy change when an acid and an alkali react to form one mole of water under standard conditions

Question 3

What are standard conditions??

Answer 3

298K and 101KPa

Question 4

Standard enthalpy of reaction?

Answer 4

Enthalpy change that occurs when equation quantities of materials react under standard conditions and everything in their standard state

Question 5

Standard enthalpy of formation??

Answer 5

Enthalpy change when 1 mole of a substance is formed from its elements in their natural state under standard conditions

Question 6

What does a hess’ law triangle look like when you’re given standard enthalpy changes of combustion and a reaction??

Answer 6

• The reaction you’re given goes along the top as 🔼H1.
• Carbon dioxide and water goes at the bottom in the correct molar quantities from the reactants
• arrows point down from the reactants and the products to the CO2 and H2O

Question 7

What does a hess’ law triangle look like when you’re given standard enthalpies of formation, and you want to work out the enthalpy change for the combustion of something

Answer 7

• equation you’re given alone the top
• elements in their natural state alone the bottom, make sure one mole of product can be formed from them
• arrows pointing up from elements to products and reactants of top equation (ignored oxygen)