Question

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

Answer 1

Some assumptions have to be made...

Explanation:

We must first know the starting temperature of the methanol. Let's assume it is stored in a lab at a normal 22 degrees Celcius. Lets also assume that the 2kg of the Methanol we are going to heat is entirely pure. (E.g not diluted methanol but 100% stock solution)

The specific heat capacity of Methanol is `2.533 J g^-1 K^-1` According to this chart. The boiling point of methanol is 64.7 degrees Celcius. Thus to make it boil we must heat it up by 42.7 degrees.

Using the equation:

`Q=mcDeltaT`
Where Q is the energy input in Joules, m is the mass in kg ( I will use grams as the heat capacity found applies to grams). C is the specific heat capacity and `DeltaT` is the temperature change in Celcius/Kelvin, as one step on the Kelvin scale is equal to that on one step on the Celcius scale.

2kg=2000 grams and then we plug in the rest:

`Q=2000 times 2.533 times 42.7`

`Q=216318 J approx 216.3 kJ`