Calculate the Heat Absorbed?

Question

6.84g of NaNO3 are placed into 288g of H2O and the temperature rises 12 degrees Celsius.

Find:

(a) the heat absorbed by the water

(b) the # of mol of salt used

(c) the heat of solution of the salt in J/mol and kJ/mol

Please help, I'm really unsure of what to do.

Answer 1

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one equation you need is the famous

Q = m*c*delta T the eenergy is the product of the mass, the temp change, and the specific heat of the material being warmed up.

so, Q = 288 * 4.18 * 12 = 14446 joules = 14.446 kJ

one mole of sodium nitrate would have a mass of 85 grams (23 + 14 + 16 + 16 + 16)

1 gram os sodium nitrate represents one 85th of a mole

so 6.84 grams is 6.84 85ths of a mole

Now you need to imagine what the temperature rise would be if you used a mole of sodium nitrate.

Or better still, what energy would be given out if you dissolved a mole of NaNO3

To calculate it you need to divide the joules (or kilojoules) by the moles.

it's all there in the unit of the answer; kilojoules per mole.