Methanol has a ΔHvap = 35.3 kJ/mol

CH3OH. Calculate the change in heat, q, when
50.0 g methanol condenses? Caution! Is q + or -?

it releases heat when it condenses.

a. calculate the moles in 50g.
moles= 50/molmass
calculate the molmass of methanol.

b. heat= moles*(-Hevap)

To calculate the change in heat (q) when 50.0 g of methanol condenses, you need to use the formula:

q = m * ΔHvap

where:
q is the change in heat (in joules),
m is the mass of the substance (in grams),
ΔHvap is the heat of vaporization (in J/g or kJ/mol).

Given that the heat of vaporization (ΔHvap) of methanol is 35.3 kJ/mol, we need to convert this value into J/g. To do this, we will use the molar mass of methanol.

The molar mass of methanol (CH3OH) can be calculated as follows:

C = 12.01 g/mol
H = 1.01 g/mol (there are 4 hydrogen atoms)
O = 16.00 g/mol

Adding these together:

12.01 + (1.01 * 4) + 16.00 = 32.04 g/mol

Therefore, the molar mass of methanol is 32.04 g/mol.

To convert ΔHvap from kJ/mol to J/g, we can use the molar mass:

35.3 kJ/mol * (1000 J/kJ) / (32.04 g/mol) = 1100 J/g (approximately)

Now that we have the value for ΔHvap in J/g, we can calculate the change in heat (q):

q = m * ΔHvap
q = 50.0 g * 1100 J/g
q = 55000 J

Therefore, the change in heat (q) when 50.0 g of methanol condenses is 55000 J.

In terms of the sign, the change in heat (q) is negative (-) because condensation is an exothermic process, meaning it releases heat to the surroundings.