Chemistry Energetics

the heat content of a system

is positive

is negative

• 100 kPa 
• 25 C
• substances in their standard states

heat change/temperature change

• Q= m c DT
• and DH = Q/n
• n being the mole of the limiting reagent

• the energy required to break a mole of a covalent type of bond in a gaseous state averaged across a variety of compounds
• reactants-products
• kJ/mol
• Limitation: average taken, they must be in their standard states

is the enthalpy change for the complete combustion of one mole of a substance in its standard state in excess oxygen under standard conditions

polystyrene cup

but enthalpy change can be measured through measuring temperature chang e

• Standard enthalpy change of formation is the enthalpy change that occurs when one mole of the substance is formed from elements in their standard states
• products-reactants

psotivie ions

negative ions

enthalpy change that occurs when one mole of solid ionic compound is separated into gaseous ions under standard conditions

one mole of gaseous atoms are formed from the element in its standard state

• first is exothermic
• second is endothermic

• ions get smaller
• ions have higher charges

• is the enthalpy change when one mole of a solute is dissolved in a solvent to infinite dilution under standard conditions
• latttice+ hydration of ion + hydration of ion

• exothermic and negative
• strength of bonds between polar water molecules and the separated ions

• distribution of available energy among particles 
• DS
• products-reactants

• DHf
• and DG

• kinetic energy distribution 
• -DH/Temp

• is products of reaction-reactants of reaction
• or DH-TDS of reaction 
• negative means spontaneous 
• positive means non-spontaneous 
• happens between -30 and 30

at equilibrium