# Is q = mc delta T only for H2O?

My question is about heat calculation. I learned that q = mc delta T. Is that only for water? I'm doing a practice problem "100 g of NH3 are cooled from 100 C to 75 C. Heat capacity for ammonia gas 35.1 J/ mol *K. What is heat change?" I plugged in the mass of ammonia but the solution turned it to moles. So is q = mc delta T only for water? Why did the book's answer key convert to moles? Thank you.

No it is not only for water but each object has a different (edited see note 1) heat capacity.  So with your question delta T is 25 degrees Celsius and also 25 degrees Kelvin because the size of the degree is same for Celsius and Kelvin.  That is not the case if they give temps in Fahrenheit.  If the question gives T in Fahrenheit then you would have to convert to Kelvin.

They give you the heat capacity of NH3 gas = 35.5 J/mol*K.  Or wait can you clarify is that information they have given you or is that what you are calculating?

There is also a different type of problem with 'calorimetry' where a substance is cooled in water and the temperature of the water is measured and use the waters heat capacity.  But for ammonia gas I don't think that is this one you are solving.  But the substance might be a piece of weighed hot metal or something.

Ok heat capacity is q/deltaT

specific heat capacity is the quantity of heat needed change the temperature of a gram of substance by 1 K

specific heat capacity (c) = q/(mass x delta T)

So you can use these with both substances and mixtures.  You could have a complex matrix.

But reserved for substances is the molar heat capacity and that is only for substances.  So a substance is water.  Or ammonia gas.  But not an arbitrary mixture of the two.

molar heat capacity (C)* = q/(ammount(mol) * deltaT)

Does this make sense?  Basically it is just changing ammount (mass) you use for specific heat capacity and switching to molar heat capacity which uses amount (mol) instead.

For the same substance if you have more moles you have more mass.  Like if you have 2 grams of water or 1 gram of water you also have twice the ammount of moles in the first than the second.

*uppercase C is molar heat capacity lowercase c is specific heat capacity

note 1: edited an error.  every object has own heat capacity.  But c stands for specific heat capacity.  C for molar heat capacity.

Hi, thanks so much!

OK I think I get it. I first calculated the answer in grams, but you're saying because the units for the heat capacity the problem gave me was J/mol*K, mass wouldn't do.

Awesome. Thank you. Boron not a moron, despite my orgo prof

Ok looking at problem again you are asked to calculate heat transferred (q).  So to use the molar heat capacity you need to know the moles of ammonia.  But they tell you grams.  So how many moles in 100 g of NH3?