Enthalpy of Formation

How do you calculate Enthalpy of a reaction?

• ΔH = ΔH_products - ΔH_reactants

• ΔT = q / mC

• ΔG = ΔH -TΔS

• E = mc²

Tags

NGSS.HS-PS3-1

What is standard enthalpy of formation, ΔH_f^o?

• Heat change when 1 mole of gaseous ions is hydrated in water at 25^oC and 1 atm

• Heat change when 1 mole of compound is formed from its elements in their standard states at 25^oC and 1 atm

• Heat change when 1 mole of gaseous atom is formed from its elements at 25^oC and 1 atm

• Heat change when 1 mole of electrons is removed from 1 mole of gaseous atoms at ground state at 25^oC and 1 atm

Define standard enthalpy of combustion.

• Heat released when one mole of substance is burnt completely in excess oxygen.

• Heat absorbed when one mole of substance is burnt completely in excess oxygen under standard state.

• Heat released when one mole of substance is burnt completely in excess oxygen under standard state.

• Heat change when one mole of substance is burnt partially in excess oxygen under standard state.

Which of the following has a ΔH_f^o value of 0?

• Br₂(g)

• N(g)

• CO(g)

• Ne(g)

Which of the equation below refers to the standard enthalpy of formation, ΔH_f^o?

• Na(g) ---> Na⁺(g) + e^- ΔH = -364 kJmol^-1

• C₂H₅OH(l) + 3O₂(g) ---> 2CO₂(g) + 3H₂O (l) ΔH = - 1286 kJmol^-1

• 2C(s) + 2H₂(g) ---> C₂H₄ (g) ΔH = - 52.3 kJmol^-1

• Na⁺(g) ---> Na⁺(aq) ΔH = - 364 kJmol^-1

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

When 1.0 mole of ZnO(s) decomposes,

ZnO(s) ---> Zn(s) + 1/2 O₂(g) , enthalpy change is +348 kJ/mol.

What does this tell you about the formation of ZnO (s)?

• the formation of ZnO (s) is endothermic

• the formation of ZnO (s) is exothermic

• the formation of ZnO (s) does not require energy

• the formation of ZnO (s) absorbs heat.

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

Which statement is true regarding endothermic reactions?

• a) Temperature change is positive and enthalpy change is positive
• b) Temperature change is positive and enthalpy change is negative
• c) Temperature change is negative and enthalpy change is positive
• d) Temperature change is negative and enthalpy change is negative

Tags

NGSS.HS-PS1-4

Endothermic reactions feel

• warm
• cold

Tags

NGSS.HS-PS1-4

Define 'Enthalpy'

• a) Energy stored in the movement of molecules in a substance
• b) The opposite of temperature
• c) The temperature of a molecule
• d) Energy stored in the chemical bonds in a substance

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

Heat is measured in 

• joules
• grams
• degrees celcius