Enthalpy 1 Flashcards
Exothermic
A reaction when delta H is negative. Energy is transferred from the system to the surroundings, so the temperature of the surroundings increases as they gain energy.
Endothermic
A reaction where delta H is positive. Energy is transferred from the surroundings to the system, so the temperature of the surroundings decreases as they loose energy.
Energy profile diagram of an exothermic reaction
Products
-------------------------Energy profile diagram of an endothermic reaction
Products
———————-
Activation energy
The minimum energy required for a reaction to take place
Standard conditions
Units= KJmol-1 and mol-1 Pressure = 100 kPa Temperature= 298K Concentrations = 1 mol dm-3
Standard state
The physical state of a substance under standard conditions
Standard enthalpy change of a reaction
The enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation, under standard states and conditions
Enthalpy change of formation
The enthalpy change that takes place when one mole of a compound is formed from its elements under standard conditions and in their standard states
Enthalpy change of combustion
The enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions and in their standard states
Enthalpy change of neutralisation
The energy change that accompanies the reaction of an acid and a base to form one mole of water under standard states and under standard conditions.
Equation for enthalpy change
q= mc(deltaT)
m is the mass of the thing you are heating up
T is temperature change
c is the specific heat capacity for water this is 4.18
Why might delta C from experimental data not be accurate
Heat loss to the surroundings (excluding water). Incomplete combustion. Non standard conditions. Evaporation of methanol from the wick
Average bond enthalpy
The energy required to break a mole of a specific bond. Bonds broken - Bonds made
How do you carry out enthalpy change with given values
Product - reactants
