Help chemistry a level

Help, I don’t get how I would know that the Enthalpy of reaction is plus or minus 4 times Enthalpy change of vapourisation. I don’t get the part in the mark scheme that I’ve circled

(edited 1 year ago)

Reply 1

charco

Study Forum Helper

Original post by Alevelhelp.1

Help, I don’t get how I would know that the Enthalpy of reaction is plus or minus 4 times Enthalpy change of vapourisation. I don’t get the part in the mark scheme that I’ve circled

Combustion enthalpies are usually quoted for at 298K. Under these conditions water is a liquid.
But the equation given shows water as a gas.
So you must factor into the equation the energy needed to change liquid water into gaseous water (the vaporisation enthalpy). As there are four mol of water in the equation, then you must multiply it by 4.