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enthalpy
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enthalpein
(to warm)
enthalpy Represented by the symbol,
H.
enthalpy refers
to the energy transferred under constant pressure.
enthalpy Often referred to as the
heat
content
enthalpy
cannot
be measured but it is possible to measure the
change in enthalpy or heat content, ΔH
Enthalpy change, ΔH, that accompanies chemical
reaction is called
heat
of reaction.
enthalpy
is the net energy change resulting from the breaking
and making of bonds.
ΔH =
Hproducts
- Hreactants
The sign of ΔH indicates the direction of
heat
transfer.
A positive value indicates that the system
absorbs
heat from the surroundings and is,
endothermic.
A negative value indicates that heat is
released
by the system, hence, the process is exothermic.
Enthalpy also indicates the amount of heat stored as
potential
energy.
in an exothermic reaction, the
products will have a
lower
energy than the reactants.
A balanced equation in which the value of ΔH, with the
appropriate sign, is usually written at the
right
side.
Balanced chemical equation:
CH4(g) + 2O2(g) → CO2(g) +
2H2O(l)
+
890.4
kJ
Thermochemical equation:
CH4(g) +
2O2(g)
→ CO2(g) +
2H2O(l)
ΔH = −890.4kJ
it is negative because heat is at the product side meaning the system produced heat meaning it is
exothermic
Balanced
chemical equation:
CaCO3(s) + 177.8 kJ → CaO(s) + CO2(g)
Thermochemical equation:
CaCO3(s) → CaO(s) + CO2(g) ΔH = 177.8 kJ
it is
positive
because the caco3 is
heated
resulting to the product meaning the substance is heated by the
surrounding
meaning it is
endothermic
Calorimetry
Concerned
with the
measurement
of heat
changes or
heat
flow in a chemical
reaction.
The device used to measure heat changes is
a
calorimeter.
hesss
law states that ΔH = ΔH1 +
ΔH2
+
hey
hello
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