A sample of gas absorbs $$4000 \mathrm{~kJ}$$ of heat and surrounding does $$2000 \mathrm{~J}$$ of work on sample. What is the value of $$\Delta U$$ ?

If $$38.55 \mathrm{~kJ}$$ of heat is absorbed, when 6.0 of $$\mathrm{O}_2$$ react $$\mathrm{CIF}$$ according to reaction.

$$2 \mathrm{CIF}(g)+\mathrm{O}_2(g) \longrightarrow \mathrm{Cl}_2(g)+\mathrm{OF}_2(g)$$

What is the standard enthalpy of reaction?

An ideal gas expands isothermally and reversibly from $$10 \mathrm{~m}^3$$ to $$20 \mathrm{~m}^3$$ at $$300 \mathrm{~K}$$, performing $$5.187 \mathrm{~kJ}$$ of work on surrounding, calculate number of moles of gas used.

"The mass and energy both are conserved in an isolated system", is the statement of