Question

Ethyl chloride (C2H5Cl) boils at 12∘C. When liquid C2H5Cl under pressure is sprayed on a room-temperature (25∘C) surface in air, the surface is cooled considerably.Assume that the heat lost by the surface is gained by ethyl chloride. What enthalpies must you consider if you were to calculate the final temperature of the surface?

Check all that apply.

The specific heat of the solid surface

The enthalpy of vaporization of C2H5Cl(l)

The specific heat of C2H5Cl(l)

The specific heat of C2H5Cl(g)

Answer 1

When two materials with different temperatures come in contact the heat flow happens from warmer material to cooler material until the temperature of both objects is the same. That is to say the total heat or energy is conserved and not lost during the process.

Therefore

q_hot + q_cold = 0

When the above equation is rearranged as

q_cold = - q_hot

it indicates that the heat transferred from warmer material to cooler material is same. However the sign of heat flow values is opposite because the direction of heat flow is different for both materials.

The heat absorbed or lost over a process for any material is calculated using the following equation:

q = specific heat ( c ) x mass of substance (m) x temperature change (ΔT)

q = c x m x ΔT= c × m × (T_final − T_initial)

Hence, in a heat transfer between two materials, both materials’ specific heats and initial and final temperatures and their masses are needed for calculation as given below:

[mC_sΔT]_cold= −[mC_sΔT]_hot

Therefore in the current problem all given parameters

The specific heat of the solid surface

The enthalpy of vaporization of C2H5Cl(l)

The specific heat of C2H5Cl(l)

The specific heat of C2H5Cl(g)

are required for calculation of the final temperature of the surface.