Enthalpy Essay, Research Paper
What are the thermodynamic standard conditions? 298K, 1 atm pressure, concentration of 1mol per dm3 What is enthalpy change? The heat change measured at a constant pressure and
temperature. Define standard enthalpy of formation: The enthalpy change when a single mole of compund is formed from its elements
under standard conditions of 298K and 1atm pressure with all the reactants in
their standard states. Why is enthalpy change for exothermic reactions negative? Because energy has been released to the surroundings. The products therefore
have a lower enthalpy than the reactants and the final enthalpy is less than the
initial enthalpy. Classify as endothermic or exothermic: NaOH dissolves in water & temp. of solution rises – Exothermic Ammonium Chloride dissolves in water and temp. of surroundings drop -
Endothermic
H and O combine explosively into water – Exothermic
Liquid water condenses into ice at 0 C – Exothermic
Liquid Nitrogen boils spontaneously at room temp.- Endothermic
Why is standard enthalpy changes of combustion always negative? Because heat is always evolved, the reaction is exothermic and therefore heat
is lost to the surroundings. The energy required to break bonds is always less
than the energy released when bonds are formed.