Question

If enthalpies of formation for $ {{C}_{2}}{{H}_{4}}(g),\,\,C{{O}_{2}}(g) $ and $ {{H}_{2}}O\,\,(l) $ at $ {{25}^{o}}C $ and $ 1\,\,atm $ pressure are $ 52, $ $ -394 $ and $ -286\,\,kJ/mol $ respectively, then total enthalpy of combustion is

• A. $ +1412\,\,kJ/mol $
• B. $ +141.2\,\,kJ/mol $
• C. $ -141.2\,\,kJ/mol $
• D. $ -14.2\,\,kJ/mol $

Answer 1

Answer: (C)

Given: Enthalpies of $ {{C}_{2}}{{H}_{4}}(g),\,\,C{{O}_{2}}(g) $ and $ {{H}_{2}}O\,\,(l) $ $ 52,\,\,-394 $ and $ -286 $ respectively. We know that $ {{C}_{2}}{{H}_{4}}+3{{O}_{2}}\xrightarrow{{}}2C{{O}_{2}}+2{{H}_{2}}O $ Therefore, total enthalpy of their combustion $ =2\times (-394)+2\times (-286)-(52) $ $ =-1412\,\,kJ/mol $