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# chemistry 17

### chpt 17

Enthalpy reaction the quantity of energy transferred as heat during a chemical reaction.
enthalpy formation enthalpy change that occurs when one mole of a compound is formed from its elements in their standard state at 25 degrees and 1 atm.
enthalpy combustion the energy released as heat by the complete combustion of a specific amount of a substance at a constant pressure or constant volume.
entropy measure of the randomness or disorder of a system
entropy decrease decrease is when the particles are at low random, Ex freezing water you are converting it froma liquid to a solid so therefore forcing the particles to be more at random.
entropy increase EX. paper burning its more at random so therefore an increase in entropy because you are converting the solid paper to another state of matter.
thermochemical equations 2h2+o2-->2h2o+483.6KJ of energy
free energy change delta G, a system that is defined as the difference between the change in enthalpy, delta H, and the product of the kelvin temperature and the entropy change(t Delta s)
free energy equation delta (G)=HR-T(delta S)
Reaction 1 if T and S are both positive the reaction will only occur IF it is at high temperature and the sum is great then HR.
Reaction 2 HR (+) and S (-) and If (G) is positive the reaction will never occur! but if (G) is negative the reaction will occur.
Reaction 3 HR (-) delta S (-) reaction can still take place.
Heat of FOrmation H2+ .5o2-->H2o +241.8 KJ the amount of energy changes that occur when a compound is freed from its elements is an indication that formed when it is a compound. The more energy thats given off when its formed the more stable the compound.
hess's Law the overall enthalpy change in a reaction is equal to the sum of enthalpy changes for the individual steps in the process.
Created by: this_isme