[rtblue]

100mL of water is poured into a Styrofoam cup. 4g of solid NaOH is added to this cup. A reaction occurs, and the change in temperature is 9.2 degrees celcius. Calculate the amount of heat released.

I am almost certain that q=smt will be used here, but I am unsure of a few things:

Do i need to account for the mass of water in my mass variable?
Do i need to have two seperate equations, one for NaOH and one for water, and then subtract?
Will i use 4.184 for specific heat?

[horsebox]

Yeah you definitely need to account the mass of the water, the mass of the NaOH doesn't matter cuz they've already told you the change in temperature produced by it. Remember 1ml of water weighs 1g so you've 100g of water there. The specific heat capacity of water is 4.2 J/g˚C. You're trying to find out how many joules it took to raise the temperature of 100g of water by 9.2 degrees so you just plug all this into your formula:
q = (4.2)(100)(9.2) joules.

I dunno what this reaction they're talking about is. NaOH will just ionise in the water and the heat produced is just the enthalpy change of solution. Since this is just high school chemistry I doubt you have to take into consideration the mass of the NaOH and the heat capacity of an NaOH solution.

[Borek]

Mass of NaOH should be added to mass of water and you should treat it as mass of solution.

[horsebox]

Mass of NaOH should be added to mass of water and you should treat it as mass of solution.

Then you have to find the specific heat capacity of whatever molarity solution you have though don't you?

[Borek]

Yes, but it is a common approach to calculate total mass and assume specific heat of water.

One may check something like CRC handbook or International Data Tables (owned by Knovel now) for a correct value of specific heat of 1M NaOH solution. Or one may even use density tables to calculate exact concentration, but taking into account accuracy of the procedure it doesn't make much sense.