Caculate the heat of hydration of Copper sulphate to form hydated copper sulphate GIVEN that the heat of Solution Of hydrate Copper Sulphate are -66.5KJ + 11.0 KJ
Answers
Answer:
Hess’s law states that total enthalpy change for a reaction is
independent of the route by which the chemical change takes place
Hess’s law is a version of the first law
of thermodynamics, which is that
energy is always conserved.
2H (g) + 2Cl(g)
H2 + Cl2
2HCl (g)
a
b
ΔH
On an energy level diagram the directions of the arrows can
show the different routes a reaction can proceed by
In this example one route is arrow ‘a’
The second route is shown by arrows ΔH plus arrow ‘b’
So by applying Hess’s law
a = ΔH + b
And rearranged
ΔH = a - b
H+
(g) + Br -
(g) H+
(aq) + Br -
(aq)
H (g) + Br (g) HBr (g)
a
c
d
ΔH
Interconnecting reactions can also be shown diagrammatically.
In this example one route is arrow ‘a’ plus ΔH
The second route is shown by arrows ‘c’ plus arrow ‘d’
So a+ ΔH = c + d
And rearranged
ΔH = c + d - a
The two routes must have the same starting point and the
same end point
Energy
CuSO4
(aq)
CuSO4 (s) + 5H2O (l) CuSO4
.5H2O (s)
+ 11kJmol-1 = -66.1 kJmol-1
∆H reaction
+ aq + aq
∆H reaction
+11kJmol-1 -66.1 kJmol-1
∆H reaction = -66.1 - 11
= -77.1 kJmol-1
This Hess’s law is used to work out the
enthalpy change to form a hydrated salt
from an anhydrous salt.
This cannot be done experimentally
because it is impossible to add the exact
amount of water to hydrate the copper
salt and it is not easy to measure the
temperature change of a solid turning into
another solid.
Often Hess’s law cycles are used to measure the enthalpy change for a reaction that cannot be measured
directly by experiments. Instead alternative reactions are carried out that can be measured experimentally.
Explanation: