Topic 5/15: Energetics Flashcards
Define exothermic.
- Heat is released to the surroundings ➜ Negative enthalpy values
- Products are more stable than the reactants
- E.g. bond forming (removing heat brings atoms closer together), gas ➜ liquid ➜ solid, combustion, neutralization, displacement, precipitation
Define endothermic.
- Heat is absorbed from the surroundings ➜ Positive enthalpy values
- Products are less stable than the reactants
- E.g. bond breaking (adding heat separates atoms), solid ➜ liquid ➜ gas
Outline standard enthalpy of formation.
- The energy change when one mole of a compound is formed from its elements in their standard states under standard conditions
- Products - Reactants
Outline standard enthalpy of combustion.
- The energy released when one mole of a compound is completely burned in excess oxygen under standard conditions with no change in pressure
- Always exothermic as heat is released
- Reactants - Products
Outline enthalpy change equation.
Q=mcT
- Q=heat change
- m=mass (mass of water unless specified)
- T=temperature change (initial - final)
Outline standard enthalpy of neutralization.
- The enthalpy change when a strong acid and base react together to form one mole of water under standard conditions
- Always exothermic
Outline Hess’s Law.
Regardless of multiple stages or steps, the total enthalpy change for the reaction is the sum of all changes
Define average bond enthalpy.
The energy required to break one mole of the same type of bond in the gaseous state averaged over a variety of similar compounds
Outline the oxygen present in the atmosphere.
- Normal oxygen and ozone
- Bonds in O2 are stronger than O3
- O2 requires higher energy UV radiation (shorter wavelength) to break
Define lattice enthalpy.
- The energy required when one mole of an ionic compound is formed from its gaseous ions
- Cannot be measured because gaseous ions do not combine directly to form a compound
- Requires use of the Born-Haber cycle
Define atomization enthalpy.
The energy change to make one mole of gaseous atoms from its elements
Define enthalpy of solution.
The enthalpy change when one mole of an ionic compound is dissolved in water to infinite dilution
Define enthalpy of hydration.
The enthalpy change when one mole of gaseous ions dissolve to give an infinitely dilute solution.
Define entropy.
- The distribution of available energy among the particles in a system/Measure of disorder of a system
- A more disordered system gives a more positive entropy
- A more ordered system gives a negative entropy
- Products - Reactants
Outline the factors that increase the entropy of a system.
- Changes of state
- Gas has the highest entropy
- Solids have the least entropy
- Gas > Liquid > Solids
- Increased number of particles (increasing conc.)
- Increased temperature (increases particle movement)
- More complicated structure
- Dissolution (dissolving) of an ionic compound
