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# How to calculate with chemical equations

- Convert all given data to moles. - Raison with moles moles and the meaning of the equation to have the result expressed in moles. - Convert the result to the desired unit.

Example: Find the mass (g) of water which may be obtained from 1.12 L ( at normal conditions ) of oxygen ! 1) Equation $2H_2$ $+$ $O_2$ $\longrightarrow$ $2H_2O$ 2) Conversion into moles: $n_{O_2}$ $=$ $\frac{1,12}{22,4}$ $=$ $0,05$ 3) Meaning of the equation expressed in moles: 2 mol $H_2$ + 1 mol $O_2$ → 2 mol $H_2O$ 4) Raisoning: If 1 mol of $O_2$ gives 2 mol of $H_2O$, therefore 0,05 moles $O_2$ give $0,05\cdot 2 = 0,1$ mol $H_2O$ 5) Conversion of the result into g: $m_{H_2O}$ $=$ $n_{H_2O}\cdot M_{H_2O}$ $=$ $0,1\cdot18=1,8 g$

Exercises