Enthalpy changes Flashcards
What is enthalpy change?
Heat energy transferred in a reaction at constant pressure
What are standard conditions?
100kpa and a stated temperature
What ^H value do exothermic reactions have?
Negative delta H value because heat energy is given out
What delta h value do endothermic reactions have?
Positive delta H values because heat energy is absorbed (gains energy)
What is the definition of enthalpy change of formation?
The enthalpy change when 1 mole of a compound is formed from its elements
e.g Ca + Cl –> CaCl2
What is the definition of enthalpy change of atomisation of an element?
The enthalpy change when 1 mole of gaseous atoms is formed from an element
e.g 1/2 Cl2 –> Cl
What is the definition of enthalpy change of atomisation of a compound?
Is the enthalpy change when 1 mole of a compound is converted to gaseous atoms
e.g NaCl –> Na (g) + Cl (g)
What is the definition of first ionisation energy?
The energy needed to change 1 mole of gaseous atoms into 1 mole of gaseous 1+ ions
e.g Mg(g) –> Mg+ (g) + e-
What is the definition of second ionisation energy?
The energy needed to change 1 mole of gaseous 1+ ions atoms into 1 mole of gaseous 2+ ions
e.g Mg+(g) –> Mg2+ (g) + e-
What is the definition of electron affinity?
The energy needed to change 1 mole of gaseous atoms into 1 mole of gaseous 1- ions
E.g O(g) + e- –> O-(g)
What is the definition of second electron affinity?
The energy needed to change 1 mole of gaseous 1- ions into 1 mole of gaseous 2- ions e.g O- (g) +e- –> O2-(g)
What is the definition of lattice enthalpy?
The enthalpy change when 1 mole of a solid ionic compound is formed from its gaseous ions
E.g Na+ (g) + Cl- (g) –> NaCl (s)
Define the enthalpy change of hydration
The enthalpy change when 1 mole of gaseous ions is dissolved in water
Na + (g) –> Na+ (aq)
Define the enthalpy change of solution
The enthalpy change when 1 mole of solute is dissolved in a solvent, such as water
E.g NaCl(s) –> NaCl(aq)
