Calculate the change in internal energy of the system if work done by the system is 18 joule and absorbs heat 50 joule in a particular reaction.

Equal masses of helium and oxygen are mixed in an empty container at $25^{\circ} \mathrm{C}$. What is the fraction of the total pressure exerted by helium?

What is the number of oxygen atoms bonded to chlorine in its strongest oxoacid?

Dissociation constant of 0.01 M weak acid is $10^{-4}$. What is percent dissociation of acid?