Enthalpy: Mr D / Ms. R

Question 1

What is meant by STANDARD ENTHALPY CHANGE of FORMATION?

Answer 1

• Enthalpy Change that takes place when 1 MOLE of a compound
  -Is formed from its ELEMENTS under STANDARD CONDITIONS
• With ALL PRODUCTS and REACTANTS in their standard rates

Question 2

What is meant by the STANDARD ENTHALPY CHANGE of COMBUSTION?

Answer 2

• Enthalpy Change that takes place when 1 MOLE of substance
• Reacts COMPLETELY with O2 under STANDARD CONDITIONS
• With ALL PRODUCTS & REACTANTS in their standard rates

Question 3

What is meant by ENTHALPY CHANGE OF REACTION?

Answer 3

• Enthalpy Change for a reaction in MOLAR QUANTITIES
• In CHEMICAL EQUATION under STANDARD CONDITIONS
• With ALL PRODUCTS & REACTANTS in their standard rates

Question 4

What is HESS’S LAW?

Answer 4

• If a reaction can take place by more than 1 route
• & the INITAL & FINAL conditions are the same
• The total Enthalpy Change is the SAME for each route

Question 5

What is the EQUATION for ENTHALPY CHANGE?

Answer 5

Q=MC change in TIME

Question 6

What is the EQUATION for BOND ENTHALPY CHANGE?

Answer 6

Bonds broken - Bonds made

Question 7

Why do we use AVERAGE VALUES of BOND ENTHALPIES?

Answer 7

Because DIFF MOLECULES need DIFF amounts of ENERGY to break BONDS

Question 8

What are 3 reasons why the value of ENTHALPY CHANGE could differ to DATA BOOK VALUES?

Answer 8

• Heat loss to surroundings
• Incomplete combustion of fuel
• Water evaporating

Question 9

What is the HESS’S LAW TRIANGLE for FORMATION?

Answer 9

REACTANTS —————-> PRODUCTS
<——– ELEMENTS ——–>

Question 10

What is the HESS’S LAW for COMBUSTION?

Answer 10

REACTANTS —————-> PRODUCTS
<——– OXIDES ——–>

Question 11

What are IONIC BONDS?

Answer 11

• STRONG ELECTROSTATIC FORCES of ATTRACTION
• Between OPPOSITELY CHARGED ions

Question 12

What are some FEATURES of an IONIC BOND?

Answer 12

• Strong, the strength is directly related to LATTIC ENTHALPY of an Ionic Compound
• High Melting Point

Question 13

What is the DEFINITION of LATTICE ENTHALPY?

Answer 13

• The ENTHALPY CHANGE for the FORMATION
• Of 1 MOLE of an IONIC COMPOUND
• Under STANDARD CONDITIONS

Question 14

What does LATTICE ENTHALPY MEASURE?

Answer 14

• The STRENGTH of IONIC BONDING in a GIANT IONIC LATTICE
• As bonds are MADE between OPPOSITELY CHARGED (g) IONS
  –> The ENTHALPY CHANGE will always be (-)VE

Question 15

How can LATTICE ENTHALPY be CALCULATED?

Answer 15

• It CANNOT be calculated directly
• But it can be through HESS’S LAW

Question 16

What is the DEFINITION of LATTICE FORMATION ENTHALPY?

Answer 16

• The ENTHALPY CHANGE when 1 MOLE
• Of a SOLID IONIC COMPOUND is formed
• From its GASEOUS IONS

Question 17

What is the DEFINITION of ENTHALPY CHANGE OF ATOMISATION OF AN ELEMENT?

Answer 17

• The ENTHALPY CHANGE when 1 MOLE
• Of GASEOUS ATOMS is formed from an ELEMENT
• In its STANDARD STATE

Question 18

What is the DEFINITION of FIRST ELECTRON AFFINITY?

Answer 18

• The ENTHALPY CHANGE when 1 MOLE
• Of GASEOUS -1 IONS is made
• From 1 MOLE of GASEOUS ATOMS

Question 19

What is BOND DISSOCIATION ENTHALPY?

Answer 19

• The change when ALL BONDS of the SAME TYPE
• In 1 MOLE of GASEOUS MOLECULES are broken

Question 20

What is the ENTHALPY CHANGE OF ATOMISATION OF AN ELEMENT?

Answer 20

• Enthalpy change when 1 MOLE of a COMPOUND
• In its STANDARD STATE, is converted to GASEOUS ATOMS

Question 21

What is the FIRST ELECTRON AFFINITY?

Answer 21

• Enthalpy change when 1 MOLE of GASEOUS 1- IONS is formed
• From 1 MOLE of GASEOUS +1 IONS

Question 22

What is the ENTHALPY CHANGE OF HYDRATION?

Answer 22

• Enthalpy change when 1 MOLE of AQEOUS IONS
• Is formed from GASEOUS IONS

Question 23

What is the ENTHALPY CHANGE OF SOLUTION?

Answer 23

• Enthalpy change when 1 MOLE of an IONIC SUBSTANCE
• DISSOLVES in enough SOLVENT to form an INFINITELY DILUTE solution