Energetic Flashcards
Enthalpy
Heat energy stored in a chemical reaction as reactants/products. Can’t be measured but enthalpy change can
Enthalpy change
Enthalpy of products - enthalpy of reactants (KJmol^-1)
Exothermic reaction
Energy is given out to surroundings. Surroundings increase in tempeture. Reactants have more energy than the products so enthaply change is negative
Endothermic reactants
Energy is taken in from surroundings. Surroundings decrease in temperature. Products have more energy than the reactants so enthalpy change is positive.
Standard enthalpy change
Enthalpy change of a specific reaction under standard conditions with species in standard state
Standard conditions
1kpa
298K
1 mol dm-3
Standard enthalpy of formation
The enthalpy change when one mole of a compound is formed from is constituent elements with all the reactants and products in their standard states under standard conditions
Enthalpy of neutralisation
The enthalpy change when one mole of water is formed from its ions in dilute solution
Enthalpy of combustion
The enthalpy change when one mole of a substance is burned completely in excess oxygen with all the reactants and products in their standard states under standard conditions
Enthalpy of reaction
The enthalpy change when substances react under standard conditions in quantities given by the equation of the reaction
Calorimetry equations
q = m x c x /\T
/\H =q/mol
Reasons for inaccurate results calorimetry
- Incomplete combustion
- Heat loss to surroundings
- Non-standard conditions
- Evaporation of water/alcohol
- Heat capacity of calorimeter/thermometer not considered
How to improve calorimetry experiment
Use bomb calorimeter
- water insulates, heat loss reduced
- fuels burnt in 100% oxygen
Hess’s law
Enthalpy change of reaction is independent of the route taken
