Chemical Quantities and Energy in Chemical Reactions

A welder uses acetylene ($\mathrm{C_2H_2}$) and oxygen ($\mathrm{O_2}$) to weld metals. If 50.0 g of acetylene is combusted, how many grams of carbon dioxide ($\mathrm{CO_2}$) are produced? The balanced equation is: $\mathrm{2C_2H_2 + 5O_2 \rightarrow 4CO_2 + 2H_2O}$. (Molar masses: $\mathrm{C_2H_2}$ = 26.0 g/mol, $\mathrm{CO_2}$ = 44.0 g/mol)

Which of the following best describes an exothermic reaction?

A reaction produces 13.1 g of water ($\mathrm{H_2O}$). How many grams of oxygen ($\mathrm{O_2}$) were used? The balanced equation is $\mathrm{2H_2 + O_2 \rightarrow 2H_2O}$. (Molar mass $\mathrm{H_2O}$ = 18.0 g/mol, $\mathrm{O_2}$ = 32.0 g/mol)