5+15 energetics
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what is enthalpy?
measure of the heat energy contained in a substance
enthalpy is also ________
potential energy
the triangle means…
change
bond breaking requires energy to be _________ and bond forming requires energy to be _______
absorbed, released
the higher the enthalpy of a substance, the _____ stable it is
less
exothermic reactions result in a increase in the temperature of the _______________
surrounding
are the products or reactants more energetically stable in exothermic reactions?
products
draw an enthalpy diagram for an exothermic reaction
-
reactants of endothermic reactions are _____ energetically stable than that of the products
more
the first law of thermodynamics is: energy may be exchanged btw the ______ and the _________ but the total energy is ________
system, surroundings, constant
what are the standard conditions?
100kPa 1 moldm-3 298K
what is standard state?
the most pure, stable state of a substance measured at 100kPa (and 298K)
what is the enthalpy change of formation, ∆Hºf? (defin.)
enthalpy change when one mole of a compound is formed from its elements in their standard states under standard conditions of 298K and 100kPa
what is the enthalpy change of formation is 0 for…
elements
how do you use ∆Hºf to find ∆Hºreaction
∆Hºpdts - ∆Hºrxts
what is the definition of standard enthalpy change of combustion, ∆Hºc?
enthalpy change when one mole of substance in its standard state is completely burned in excess oxygen under standard conditions
∆Hºc is always -ve/+ve
-ve
what is the standard enthalpy change of neutralisation? ∆Hºneu
enthalpy change when one mole of water is formed between the neutralisation of an acid and a base under standard conditions
why do weak acids and bases have less exothermic enthalpy change as compared to strong acids and bases?
• WA+B only slightly ionised • part of the heat evolved from neutralisation is used to dissociate WA/B
what is the equation used to calculate the amount of heat transferred out of a substance?
Q = mc∆T
what are the units for Q=mc∆T
Q – J m – g c – J g^-1K^-1 ∆T – K/Cº
in an exothermic reaction, how can ∆H be found with Q?
-Q/nlim
in an endothermic reaction, how can ∆H be found with Q?
+Qnlim
what is the specific heat capacity of water?
4.18 Jg^-1K^-1