The empirical formula, <span>C<span>H2</span></span>, has a relative molecular mass of
<span>1×<span>(12.01)</span>+2×<span>(1.01)</span>=14.04</span>
This means that the empirical formula must be multiplied by a factor to bring up its molecular weight to 70. This factor can be calculated as the ratio of the relative masses of the molecular and empirical formulas
<span><span>7014.04</span>=4.98≈5</span>
Remember that subscripts in molecular formulas must be in whole numbers, hence the rounding-off. Finally, the molecular formula is
<span><span>C<span>1×5</span></span><span>H<span>2×5</span></span>=<span>C5</span><span>H<span>10</span></span></span>
Chemical bonds are formed or broken. This is true of a chemical change, but not a physical change. A physical change is usually something that you can see, such as changing of shape or form or staying the same. However, because you cannot visibly see chemical bonds being formed or broken and because this would affect the chemical composition, it is not a physical change.
1 mole = 70.9
X mole = 140
X=1.9746 moles
X= 1.98 when rounded to 3 significant figures.