energetics

Question 1

What is the definition of enthalpy change?

Answer 1

• change in heat content at constant pressure.

Question 2

What are the standard conditions?

Answer 2

• 100 kpa and 198 k

Question 3

What is the transition state?

Answer 3

• the point where some bonds are being broken and some are being made.. it is high energy and unstable
• the highest point on the bond enthalpy diagram

Question 4

What is the standard enthalpy of formation?

Answer 4

• The enthalpy change when 1 mole of a substance is formed from its constituent elements, with all reactants and products in standard states under standard conditions.
• you are only allowed to make one mole of the product so you need to balance the equation accordingly.

Question 5

What is the enthalpy change of an element?

Answer 5

0 You don’t need energy to make an element.

Question 6

What is the standard enthalpy change of combustion?

Answer 6

• The enthalpy change when one mole of a substance is completely burned in oxygen with all reactants and products in standard states under standard conditions.
• Don’t forget that carbon atoms go around alone and gases go in pairs!

Question 7

What is the standard enthalpy change of neutralisation?

Answer 7

• enthalpy change when 1 mole of water is formed in a reaction between an acid and alkali under standard conditions
• Acids and alkalis form salt and water

Question 8

What is the equation for the enthalpy change?

Answer 8

H = q/ moles in reaction.
- If the reaction is exothermic, then there has to be a negative symbol in front of the number.

Question 9

How do you figure out q?

Answer 9

• q (energy required ) = mass of liquid heated (m) x specific heat capacity (c) x change in temperature of liquid.