Energetics Flashcards
1.
Hess’s Law
The enthalpy change for a chemical reaction is the same, regardless of the route taken from reactants to products.
Standard Enthalpy of Formation, ∆Hɵf
The enthalpy change when one mole of a compound is formed from its elements under standard conditions, all reactants and products in their standard states.
Standard Enthalpy of Combustion, ∆Hɵc
The enthalpy change when one mole of a compound is completely burned in oxygen under standard conditions, all reactants and products in their standard states.
Standard Enthalpy of Atomisation, ∆Hɵat
The enthalpy change when one mole of gaseous atoms is formed from an element in its standard state.
First Ionisation Enthalpy, 1st∆Hɵi
The standard enthalpy change when one mole of electrons is removed from one mole of gaseous atoms to give one mole of gaseous ions each with a single positive charge.
Second Ionisation Enthalpy, 2nd∆Hɵi
The standard enthalpy change when one mole of electrons is removed from one mole of gaseous 1+ ions to give one mole of gaseous ions each with a 2+ charge.
First Electron Affinity, 1st∆Hɵae
The standard enthalpy change when one mole of gaseous atoms is converted into a mole of gaseous ions, each with a single negative charge under standard conditions.
Second Electron Affinity, 2nd∆Hɵae
The standard enthalpy change when one mole of electrons is added to a mole of gaseous ions each with a single negative charge, to form a mole of ions each with a two negative charge.
Lattice Formation Enthalpy ΔHLFΘ
The standard enthalpy change when one mole of solid ionic compound is formed from its gaseous ions.
Lattice Dissociation Enthalpy ΔHLDΘ
The standard enthalpy change when one mole of solid ionic compound dissociates into its gaseous ions.
Standard Enthalpy of Hydration ΔHhydΘ
The standard enthalpy change when one mole of gaseous ions is converted into one mole of aqueous ions.
Standard Enthalpy of Solution ΔHsolΘ
The standard enthalpy change when one mole of solute dissolves in enough solvent to form a solution in which the ions are far enough apart not to interact with each other.
Mean Bond Enthalpy ΔHΘ
The enthalpy change when one mole of gaseous molecules each break a covalent bond to form two free radicals, averaged over a range of compounds.
Define enthalpy change
The change in heat energy at constant pressure
What are standard conditions?
100 kPa or 1 atmosphere (1atm.) pressure and a temperature of 298K (25 degrees C)
What is the definition of activation energy?
the minimum energy needed to start a reaction
How can enthalpy changes be calculated using the equation?
enthalpy of products - enthalpy of reactants
What is the name of the process used to determine the enthalpy changes of chemical reactions?
calorimetry
How can calorimetry be used to calculate energy change (q)?
An experiment is carried out and the change in temperature is measured. This is used to calculate the energy change (q) using the formula: q = mc∆t
In the formula q = mc∆t what are the different components and their standard units?
q = energy (J)
m = mass (g)
c = specific heat capacity
∆t = change in temperature (in kelvin or degrees C)
What is true about all values of enthalpy of combustion?
they are negative because combustion reactions are exothermic, giving out energy
Suggest reasons why a student’s measured value for enthalpy of combustion is different from a data book value
- incomplete combustion
- heat transfer to the atmosphere
- the heating up of (any of the equipment) is not taken into account
- evaporation of the alcohol/water
- experiment not done under standard conditions
Explain why the enthalpy of hydration of fluoride ions is more negative than the enthalpy of hydration of chloride ions
- fluoride ions are smaller
- so fluoride ions are more strongly attracted to the electron deficient H in water
