$25 \mathrm{kJ}$ of work is done on the system and it releases $10 \mathrm{kJ}$ of heat. What is $\mathrm{\Delta U}$?

Given the thermochemical equation, ${\mathrm{C}}_2{\mathrm{H}}_2\left(\mathrm{g}\right)+\frac{5}{2}{\mathrm{O}}_2\left(\mathrm{g}\right)⟶2{\mathrm{CO}}_2\left(g\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right); {\mathrm{\Delta }}_{\mathrm{r}}\mathrm{H}°=-1300 \mathrm{kJ}$. Write thermochemical equations when coefficients of substances are multiplied by $2$.

Given the thermochemical equation, ${\mathrm{C}}_2{\mathrm{H}}_2\left(\mathrm{g}\right)+\frac{5}{2}{\mathrm{O}}_2\left(\mathrm{g}\right)⟶2{\mathrm{CO}}_2\left(\mathrm{g}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right); {\mathrm{\Delta }}_{\mathrm{r}}\mathrm{H}°=-1300 \mathrm{kJ} {\mathrm{mol}}^{-1}$. Write thermochemical equations when equation is reversed.

Write thermochemical equation for complete oxidation of one mole of ${\mathrm{H}}_2\left(\mathrm{g}\right)$. Standard enthalpy change of the reaction is $-286 \mathrm{kJ}$. Is the value $-286 \mathrm{kJ}$, enthalpy of formation or enthalpy of combustion or both? Explain.

State whether $\mathrm{\Delta S}$ is positive, negative or zero for the following reactions, $2{\mathrm{H}}_2\left(\mathrm{g}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)⟶2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$.

State whether $\mathrm{\Delta S}$ is positive, negative or zero for the following reactions, ${\mathrm{CaCO}}_3\left(\mathrm{s}\right)\stackrel{∆}{\to }\mathrm{CaO}\left(\mathrm{s}\right)+{\mathrm{CO}}_2\left(\mathrm{g}\right)$.