Question

While you were "sweating" your chemistry test, water vapor evaporates from your body, absorbing 50,000 J of energy. (assume no

temperature change). What mass of water evaporates?
A:O 150 g
B:O 22 g
C:11,962 g
D:O 105,000 g

Answer 1

`\boxed {\boxed {\sf B. \ 22 \ grams}}`

Step-by-step explanation:

We need to use the formula for heat of vaporization.

`Q=H_(vap)*m`

Identify the variables.

• The heat absorbed by the evaporating water is the latent heat of vaporization. For water, that is 2260 Joules per gram.

• Q is the energy, in this problem, 50,000 Joules.

• m is the mass, which is unknown.

`H_(vap)=2260 \ J/g\\Q=50,000 \ J \\`

Substitute the values into the formula.

`50,000 \ J=2260 \ J/g*m`

We want to find the mass. We must isolate the variable, m.

m is being multiplied by 2260 J/g. The inverse operation of multiplication is division. Divide both sides by 2260 J/g.

`(50,000 \ J)/(2260 \ J/g) =(2260 \ J/g*m)/(2260 \ J/g)`

`(50,000 \ J)/(2260 \ J/g) =m`

Divide. Note that the Joules (J) will cancel each other out.

`(50,000 \ )/(2260 \ g) =m`

`22.1238938 \ g =m`

Round to the nearest whole number. The 1 in the tenth place tells us to leave the number as is.

`22 \ g \approx m`

The mass is about 22 grams, so choice B is correct.