When a substance is changing state, its temperature remains constant. This is because energy is used to increase/decrease kinetic energy of the molecules of the substance, increasing/decreasing the inter-molecular distance and overcoming the energy bonds present between the molecules. Therefore, no energy is used to raise the temperature of the substance and therefore it remains constant
Answer : The correct option is, (c) 79.62
Explanation :
The formula used for percent humidity is:
..........(1)
The formula used for relative humidity is:
...........(2)
where,
= partial pressure of water vapor
= vapor pressure of water
p = total pressure
First we have to calculate the partial pressure of water vapor by using equation 2.
Given:
![p=750mmHg](https://tex.z-dn.net/?f=p%3D750mmHg)
![p^o_v=17.5mmHg](https://tex.z-dn.net/?f=p%5Eo_v%3D17.5mmHg)
Relative humidity = 80 % = 0.80
Now put all the given values in equation 2, we get:
![0.80=\frac{p_v}{17.5mmHg}](https://tex.z-dn.net/?f=0.80%3D%5Cfrac%7Bp_v%7D%7B17.5mmHg%7D)
![p_v=14mmHg](https://tex.z-dn.net/?f=p_v%3D14mmHg)
Now we have to calculate the percent humidity by using equation 1.
![\text{Percent humidity}=0.80\times \frac{750-17.5}{750-14}\times 100](https://tex.z-dn.net/?f=%5Ctext%7BPercent%20humidity%7D%3D0.80%5Ctimes%20%5Cfrac%7B750-17.5%7D%7B750-14%7D%5Ctimes%20100)
![\text{Percent humidity}=79.62\%](https://tex.z-dn.net/?f=%5Ctext%7BPercent%20humidity%7D%3D79.62%5C%25)
Therefore, the percent humidity is 79.62 %