Enthalpy Flashcards
What is the definition of:
Enthalpy Change
Standard Enthalpy Change
Standard State
What are the standard conditions?
Change in heat at constant pressure
Enthalpy change when all products and reactants are in their standard States
An elements pure most stable form at 298K 100kPa
Mol 298K 100kPa
Why is an enthralpy value for MgO not found in data books?
Forms MgOH which is insoluble
Define:
The Standard Enthalpy of Formation
Show an example of an equation for this using sodium and chlorine.
The Enthalpy change when one mile of a covalent compound is formed from its constituent elements under standard conditions, 298K 100kPa, all products and reactants in their standard States.
Na(s) + 1/2 Cl2(g) –> NaCl(s)
Define:
The Standard Enthalpy of Ionisation
Give an equation for this using sodium.
Is this endothermic or exothermic?
Why?
Why is the second greater?
The Enthalpy change when one mole of electrons is removed from one mole of atoms in the gaseous form to form one mole of gaseous uni positive cations.
Endothermic
Because energy is required to overcome the attraction between the positive nucleus and the leaving negative electron
Because the election is now being removed from a positively charged ion
Define:
The Standard Enthalpy of Atomisation
Write an equation for this using sodium.
What is this the same as for an atomic solid?
Why is this equal to half the bond dissociation of a diatomic molecule?
Draw an example using chlorine.
Is it endo or exo and why?
The Enthalpy change when one mole of gaseous atoms are formed from its constituent element in their standard state under 298K 100kPa
Na(s)–>Na(g)
The Enthalpy of sublimation
Because bond fission produces 2 mol of atoms
1/2Cl2(g)—> Cl(g)
Endo because energy is required to break bonds
Define:
The Bond Dissociation Enthalpy
Write an equation for this using 1)chlorine
2)Methane
Endo or exo?
The Enthalpy change when one mol of specific covalent bond in a specific gaseous covalent molecule is broken to form 2 gaseous free radicals
Cl2(g)—>2Cl(g)
CH4(g)—>CH3(g)+H(g)
Endo because bonds are breaking
Define:
The Electron Affinity Enthalpy
Write an equation for this using 1)Cl
2)O-
Are they usually end or exo?
Why may some of the second or third be the opposite?
The Enthalpy change when one mole of electrons is added to one mol of a gaseous species to form one mole of negatively charged ions
Cl(g) + e- –> Cl-(g)
O-(g)+e- –>O2-(g)
Usually exo
Some may be endo to overcome repulsion of now negative species and negative electron
Define:
The Lattice Enthalpy of Dissociation
Write an equation for this using sodium and chlorine.
Define:
The Latrice Enthalpy of Formation
Write an example for this using sodium and chlorine.
The Enthalpy change when one mole of an ionic compound is separated into its gaseous constituent ions
NaCl(s)—>Na+(g)+Cl-(g)
The Enthalpy change when one mole of an ionic compound is formed from its gaseous constituent ions
Na+(g)+Cl-(g)–>NaCl(s)
Define:
The Enthalpy of hydration
Write an equation for this using 1)Lithium
2)Bromine
Is this endo or exo?
Why?
The Enthalpy change when one mol of gaseous ions form one mol of aqueous ions
Li+(g)+ aq—> Li+(aq)
Br-(g)+aq—>Br-(aq)
Exo
Because energy is given out when ion dipole attractions are formed
Define:
The Enthalpy of Solution
Write an equation for this using sodium and chlorine.
What are the 2 stages involved?
How do you work it out?
The Enthalpy change when an ionic compound is dissolved in enough water to ensure the ions are far enough apart they do not interact
NaCl(s)+aq—>Na+(aq)+Cl-(aq)
Breaking up of the ionic lattice
Hydration of the separate gaseous ions
Bonds breaking-bonds making
Define:
Mean Bond Enthalpy
What is lattice dissociation a measure of?
What is bond dissociation a measure of?
What does this Enthalpy provide?
The average of several bond dissociation enthalpies of a given bond taken from a range of different compounds
Ionic strength
Covalent strength
An approximate value for overall Enthalpy changes when data is not available
