Ethalpy change

Question 1

What is an ethalpy change?

Answer 1

when you measure a heat change at constant pressure, you call it an ethalpy change

Question 2

What is standard molar enthalpy of formation?

Answer 2

• Δ_fH^θ
• standard molar ethalpy of formation is the enthalpy change when one mole of a compound is formed from its constituent elements
  
  • under standard conditions
• all reactants and products in their standard states
• e.g. H₂(g) + 1/2O₂(g) → H₂O(l)
  
  • Δ_fH^θ = -286kJ mol^-1

Question 3

What is the standard enthalpy of formation of an element?

Answer 3

by definition zero

Question 4

What is the stnadard molar enthalpy change of combustion?

Answer 4

• Δ_cH^θ
• enthalpy change when one mole of a substance is burnt completely in oxygen

Question 5

What is the standard enthalpy of atomisation?

Answer 5

• Δ_atH^θ
• enthalpy change which accompanies the formation of one mole of gaseous atoms from the element in its standard state understandard conditions
• e.g.
  
  • Mg(s) → Mg(g)
  • 1/2Br₂(l) → Br(g)

Question 6

What is the first ionisation energy?

Answer 6

• Δ_iH^θ
• standard enthalpy change when one mole of gaseous atoms is converted into a mole of gaseous ions with a single positive charge

Question 7

What is the second ionisation energy?

Answer 7

• refers to the loss of a mole of electrons from a mole of single positively charged ions

Question 8

What is the first electron affinity?

Answer 8

• Δ_eaH^θ
• standard enthalpy change when a mole of gaseous atoms is converted to a mole of gaseous ions
  
  • each with a single negative charge

Question 9

What is the second electron affinity?

Answer 9

• Δ_eaH^θ
• enthalpy change when a mole of electrons is added to a mole of gaseous ions each with a single negative charge to form ions each with two negative charges

Question 10

What is lattice enthalpy of formation?

Answer 10

• Δ_LH^θ
• standard enthalpy change when one mole of solid ionic compound is formed from its gaseous ions
• always negative

Question 11

What is the lattice enthalpy of dissociation?

Answer 11

• standard enthalpy change when one mole of solid ionic compound dissociated into its gaseous ions
• cannot be measured directly

Question 12

What is the enthalpy of hydration?

Answer 12

• Δ_hydH^θ
• standard enthalpy change when water molecules surround one mole of gaseous ions

Question 13

What is the enthalpy of solution?

Answer 13

• Δ_solH^θ
• stnadard emthalpy change when one mole of solute dissolves completely in suffiencent solvent to form a solution
  
  • in which the molecules or ions are far enough apart not to interact with each eachother

Question 14

What is mean bond enthalpy?

Answer 14

• the enthalpy change when one mole of gaseous molecules each breaks a covalent bond to form two free radicals, averaged over a range of compounds