Question 2.SP.11: Combining Heat Calculations Calculate the total heat, in jou......
Combining Heat Calculations
Calculate the total heat, in joules, needed to convert 15.0 g of liquid ethanol at 25.0 °C to gas at its boiling point of 78.0 °C. Ethanol has a specific heat of 2.46 J/g °C, and a heat of vaporization of 841 J/g.
Step 1 List the grams of substance and change of state.
Given 15.0 g of ethanol at 25.0 °C; boiling point of ethanol 78.0 °C
Specific heat 2.46 J/g °C; heat of vaporization 841 J/g
Need heat (J) to warm ethanol and change to gas at the boiling point
Step 2 Write the plan to convert grams to heat and desired unit. When several changes occur, draw a diagram of heating and changes of state.
Total heat = joules needed to warm ethanol from 25.0 °C to 78.0 °C (boiling point) + joules to change liquid to gas at 78.0 °C (boiling point)
Step 3 Write the heat conversion factors needed
Step 4 Set up problem with factors
ΔT = 78.0 °C – 25.0 °C = 53.0 °C
Heat needed to warm ethanol (liquid) at to ethanol (liquid) at 78.0 °C (boiling point):
15.0 \cancel {g}\times 53.0 \cancel {°C}\times \frac{2.46 J}{\cancel {g} \cancel {°C}} =1960 JHeat needed to change ethanol (liquid) to ethanol (gas) at 78.0 °C (boiling
point):
Calculate the total heat:
