High School

What quantity of heat, in kJ, is required to convert 40.0 g of ethanol ([tex]C_2H_5OH[/tex]) at 23.0°C to a vapor at 78.3°C (its boiling point)?

Given:
- Specific heat capacity of ethanol = 2.46 J/g°C
- [tex]\Delta H_{\text{vap}} = 39.3[/tex] kJ/mol

Answer :

the quantity of heat required to convert ethanol from a liquid at 23.0°C to a vapor at its boiling point of 78.3°C, The total = q₁ + q₂

we need to consider two steps: raising the temperature from 23.0°C to the boiling point, and then converting it from a liquid to a vapor.

Step 1: Calculating the heat required to raise the temperature:

To raise the temperature of a substance, we use the equation:

q = m * C * ΔT

where:
q = quantity of heat
m = mass of the substance
C = specific heat capacity of the substance
ΔT = change in temperature

Given that the mass of ethanol is 40.0 g and the specific heat capacity is 2.46 J/g⋅°C, we can substitute these values into the equation:

q₁ = 40.0 g * 2.46 J/g⋅°C * (78.3°C - 23.0°C)

Simplifying the equation gives us:

q₁ = 40.0 g * 2.46 J/g⋅°C * 55.3°C

Now we can calculate the value of q₁.

Step 2: Calculating the heat required for vaporization:

To convert a substance from a liquid to a vapor, we use the equation:

q = n * ΔHvap

where:
q = quantity of heat
n = number of moles of the substance
ΔHvap = enthalpy of vaporization

To calculate the number of moles, we need to use the molar mass of ethanol (C₂H₅OH). The molar mass of ethanol is 46.07 g/mol. We can use this information to determine the number of moles:

moles = mass / molar mass
= 40.0 g / 46.07 g/mol

Now we can substitute the values into the equation:

q₂ = (40.0 g / 46.07 g/mol) * 39.3 kJ/mol

Calculating the value of q₂ gives us:

q₂ = (40.0 g / 46.07 g/mol) * 39.3 kJ/mol

Finally, we can add the values of q₁and q₂to find the total quantity of heat required:

q_total = q₁+ q₂

Substituting the calculated values of q₁ and q₂, we can find the answer in kJ.

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