The enthalpy of combustion of C, $\text{H}_2$, and $\text{CH}_4$ are $-390$, $-285$ and $-890$ kJ/mol. Find the enthalpy of formation of methane.

Calculate the change in internal energy if an ideal gas expands from $0.5\ \text{dm}^3$ to $3.5\ \text{dm}^3$ at constant pressure 2 bar by absorbing 1800 J heat energy.

Which of the following processes exhibits the decrease in internal energy of a system?

There are two different solutions, A and B. The pH of solution A is 4. Find the pH of solution B having $[\text{H}^+]$ three times that of solution A.