In 1840, G.H.Hess (a Russian chemist) proposed an important generalisation of thermochemistry which is known after his name as Hess's law.
a) State Hess's law.
b) Give illustration of Hess's law.

Explain the Hess's law of constant heat summation

Sodium and chlorine combine to form sodium chloride on the basis of Hess's law. Try to find out the enthalpy of formation of sodium chloride.

Hess's law is a corollary of the first law of thermo dynamics. Comment.

a) DeltaG gives a criteria for spontaneity of reactions at a constant pressure and temperature. How is DeltaG helpful in precting the spontaneity of the reaction? b) State and explain Hess's law of constant heat summation.

Gas laws are relationship between the measureable properties of gases. Name the gas law which gives the relationship between the pressure and temperature of a fixed amount of gas at a constant volume. Draw the graph to illustrate the above gas law.

The enthalpy change in a process is the same, whether the process is carried out in a single step or inseveral steps. a) Identify tha law stated here. b) Calculate the enthalpy of formation of CH_4 from the following data : i) C_((s))+O_(2(g))rightarrowCO_(2(g)) DeltaH = -393.7kJ/mol ii) H_(2(g))+frac{1}{2}O_(2(g))rightarrowH_2O_((l)) DeltaH = -285.8kJ/mol iii) CH_(4(g))+2O_(2(g))rightarrowCO_(2(g)) DeltaH =-890.4kJ/mol