Energetics 1 Flashcards
Enthalpy (of a system)
a measure of the energy content of the system (H)
Enthalpy Change (of a reaction)
Enthalpy change is an indication of what stability?
The difference between the quantity of heat absorbed to break the bonds in the reactants and that released during the formation of new bonds in the products at constant pressure
Enthalpy change values are an indication of energetic stability, not kinetic stability
Activation Energy (of a reaction)
The minimum amount of energy that the reactant particles must possess before they can collide successfully to form products
Activation Energy values are an indication of kinetic feasibility of the reaction. Low Activation energies indicate a “kinetically favourable” reaction
Standard conditions
1 bar and 298K
Standard Enthalpy Change of Reaction (not likely to be tested)
The energy change in a chemical reaction when the molar quantities of reactants stated in the chemical equation react under standard conditions
Standard Enthalpy Change of Formation
What is the value of the standard enthalpy change of formation used for?
The energy change when 1 mole of the pure substance in a specified state is formed from its constituent elements in their standard states under standard conditions
The standard enthalpy change of formation valued is used to predict the stability of a compound relative to its constituent elements. The more negative the value of a compound, the more stable it is relative to the constituent elements and is less likely to decompose back into said elements.
Standard Enthalpy Change of Combustion
What are these values used for?
The energy released when 1 mole of the substance is completely burnt in excess oxygen under standard conditions
They are used as an indication of the energy values of fuels, The greater (more negative) the standard enthalpy change of combustion is, the better the fuel, since more heat is being liberated upon complete combustion.
Standard Enthalpy Change of Neutralisation (between an acid and a base)
The energy change when the acid and the base react to form 1 mole of water under standard conditions
Weak acids have less negative standard enthalpy changes of neutralisation as they are unable to fully dissociate to form H+ ions, as such the extra energy is required for them to fully dissociate.
