Textbook Question 4C11

[Emily_Stenzler_2H]

How much heat is needed to convert 80.0 g of ice at 0.0°C into liquid water at 20.0 °C (see Tables 4A.2 and 4C.1)?

The answer key shows that the equations for deltaH were used to solve this. Since the question is asking for heat, why do we not use the equation for q, and convert g to mol?

[BrittneyMyint1D]

Although they didn't give the pressure, I believe this reaction occurred at constant pressure so q = deltaH. For this problem, you would add the heat needed to melt ice + the heat needed to raise the temperature from 0 to 20 degrees C, so the second equation would use q = mcdeltaT. The first equation would be something like q = ndeltaH_fusion, so since the deltaH_fusion was given with moles instead of grams, you would have to convert the grams to moles for this part. Hope this helps!

[Karl Yost 1L]

The reaction occurred at constant pressure, meaning that qp=deltaH. Therefore, we can use deltaH as q.

[arisawaters2D]

Could you still use the equation q=m*Cs*deltaT?

[Felicia Wei 1B]

Could you still use the equation q=m*Cs*deltaT?

You would use that equation to find the energy needed to raise the temperature after the ice melted to 20 Celcius.

[Susanna Givan 2B]

We do use q! However, we can use H as q because this reaction occurs at constant pressure. Thus qp=H.