Question

# a) Define following      (i) First law of thermodynamics.     (ii) Standard enthalpy of formation.b) In a process 701 J of heat is absorbed by a system and 395 J of work is done by the system. What is the change in internal energy for the process?

Solution

## (a)(i) First law of thermodynamics $$\rightarrow$$The first law, also known as the law of conservation of energy, states that energy cannot be created or destroyed in an isolated system.(ii) Standard enthalpy of formation $$\rightarrow$$The standard enthalpy of formation of a compound is the change of enthalpy during the formation of $$1$$ mole of the substance from its constituent elements, with all substances in their standard states.(b) Given that the heat is absorbed by the system and work is done by the system.Therefore,$$q = 701 \; J$$$$w = -395 \; J$$Now from first law of thermodynamics,$$\Delta{U} = q + w$$$$\Rightarrow \Delta{U} = 701 + \left( -395 \right)$$$$\Rightarrow \Delta{U} = 306 \; J$$Hence the change in internal energy for the given process is $$306 \; J$$.Chemistry

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