Question

How many joules of heat must be added to a 2 kg sample of methanol for it to boil?

Answer 1

2.6 MJ

Explanation:

If you assume the initial temperature as 20 deg C, then you need to heat up methanol till the boiling point (67 deg C), known as the sensible heat and then supply the latent heat of vapourisation; thus, the total heat input is
`Q = m*C_p * dT + deltaH_v`

`m = 2 kg`;
`M_w= 32 g/(mol)`
`(mol_(methanol))= 2000/32 = 62.5 (mol)`
`m = 2 kg`;
`C_p= 79.5 J/(mol*K)`
`T_(boil) = 64.7^oC` https://en.wikipedia.org/wiki/Methanol
`deltaH_v = 38.278 (kJ)/(mol)` https://en.wikipedia.org/wiki/Methanol_(data_page)

Sensible heat =
`Q= 62.5 * 79.5*(64.7-20)`
=222103.125 J or 222.103125 kJ

Latent heat = `38.278 (kJ)/(mol)*62.5 (mol) = 2392.375 kJ`.
Total heat =
#222.103.125 +2392.375 = 2614.478125 kJ

Total heat = 2.6 MJ