Energetics Flashcards
What is an Endothermic reaction?
A reaction which absorbs heat (+ve)
Breaking of bonds
What is an exothermic reaction?
A reaction which produces heat (-ve)
Formation of bonds
In an enthalpy diagram what us stable and non stable state and their positions?
Stable- energy released-lower position
Unstable-energy gained-higher position
What is the specific heat capacity of water?
4.18kj/k kg
What is Hess’s Law?
The enthalpy change of a reaction depends only on the initial and final states of the of the reaction-independent of the route
Combustion enthalpy equation?
\ / reactants-products
Formation enthalpy equation?
\ / up- products - reactants
What is average bond enthalpy?
The mean of the enthalpy required to break a particular covalent bond in a range of molecules
-APPROXIMATE VALUES
What is the equation for average bond enthalpy
(Enthalpy of bonds broken)-(Enthalpy of bonds formed)
What is standard state?
101kPa, 298K,
1atm 25Celcius
What is standard enthalpy formation?
The enthalpy change when 1 mole of a substance is made from its elements in their standard state
Na + Cl—NaCl
What is Standard Enthalpy of Combustion?
The enthalpy change when 1 mole of a substance is completely burned in oxygen under standard conditions
What is Ionization Enthalpy?
The enthalpy change when 1 mole of gaseous 1+ ions are formed from 1 mol of gaseous atoms
Na(g)–Na+(g) + e-
What is electron affinity?
The enthalpy change when 1 mol of gaseous atoms each gain 1 electron
Cl + e—Cl-(g)
What is Bond Dissociation Enthalpy?
The breaking of a covalent bond in a gaseous molecule to form two gaseous free radicals
Cl2(g)—2Cl
CH4(g)–CH3(g) + H
What is Enthalpy of Atomization?
The Enthalpy change when 1 mole of atoms in gaseous state is formed from the element in its standard state
1/2Cl2(g)–Cl(g)
Na(s)–Na(g)
What is Lattice Enthalpy?
The separation of 1 mol of a solid ionic lattice into its constituent gaseous ions(dissociation)
NaCl(s)—Na+(g) + Cl-(g)
(Formation) (-ve) Na+(g) + Cl(g)–NaCl(s)
What is the equation for the enthalpy of formation
The sum of all steps = enthalpy of formation
What does lattice Enthalpy change with?
- Size of ions-as size getw bigger lattice enthalpy attraction gets greater because more shielding, easier to bond
- Charge on ions-the bigger the ion the bigger the lattice enthalpy
What is Entropy?
Degree of disorder
What factors increase disorder in a system? (4things)
- Increase number of particles
- Mixing of particles
- Change of state to greater distance between particles
- Increase particle movement
Equation for Entropy?
S(products)-S(reactants)
What is meant by Gibbs Free Energy?
A measure of total entropy of the universe.
Gibbs equation?
G=H-TAS/1000
