Topic 5 - Chemical energetics Flashcards
Define
Activation energy
the minimum amount of energy needed for reactant molecules to have a successful collision and start the reaction
The minimum energy required for a collision to be effective
Enthalpy Change
the change in chemical energy during a chemical reaction
State
Standard Conditions
101 kPa
298 K
Each substance involved is in its normal physical state
solutions concentration of 1.0 mol dm^-3
Standard Enthalpy Change of reaction
This is the enthalpy change when amounts of reactants as shown in the reaction equation, react together under standard conditions to give products in their standard states
H2 + (1/2) O2 → H2O
Standard Enthalpy Change of formation
This is the enthalpy change when one mole of a compound is formed from elements in their standard states under standard conditions
C + 2H2 → CH4
Standard Enthalpy Change of Combustion
This is the enthalpy change when one mol of a substance is burned in an excess of oxygen under standard conditions
C3H8 + 5O2 → 3CO2 + 4H2O
Standard Enthalpy Change of Neutralisation
This is the enthalpy change when one mole of water molecules is formed when an acid reacts with an alkali under standard conditions
HNO3(aq) + KOH(aq)→ H2O(l) + KNO3 (aq)
H^+ + OH^- → H2O
State
Hess’s Law
The total enthalpy change in a chemical reaction is independent of the route by which the chemical reaction takes place as long as the initial and final conditions are the same
Define
Standard enthalpy change of vapourisation
This is the heat needed to convert one mole of substance from liquid to gas. The substance should be at its boiling point and a pressure of 1 atm
Define
Exact Bond energy
The amount of energy required to break one mole of a specific covalent bond in the gas phase
bond dissociation energy
Describe
Average Bond Energy
The average of a number of the same type of bond but in different environments is calculated
The bonds energies are affected by other atoms in the molecule/its environment
