Question

6) Lactic Acid (C3H6O3) can be polymerized to become poly-lactic acid, an alternative for the plastic industry that does not involve the use of fossil fuels. If lactic acid is combusted, write the balanced chemical equation.

6b) Calculate the enthalpy change for the combustion of 10.0 g of lactic acid. Hint: You will need to determine the enthalpy change for the combustion of one mole of lactic acid first. You will find the following thermodynamic data useful. Is this reaction exothermic or endothermic?

Answer 1

$CH_3CH(OH)COOH+3O_2\to 3CO_2+3H_2O$

The above reaction shows Lactic acid on combustion produces carbon dioxide and water vapour

The molar mass of lactic acid is 90 g

Let the $\Delta H$ for the combustion of lactic acid be $x$

then the enthalpy change in combustion of 10 g of lactic acid will be $\frac{10}{90}x=\frac{x}{9}$