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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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