Calculate the change in enthalpy produced by dissolving 14.3 g of NaOH in 65.0 g of water if the temperature increases 49.1°C and the specific heat of water is 4.18 J/g°C
Do I have to use the 14.3g of NaOH?
q = mass H2O x specific heat H2O x delta T.
That gives you delta H for 14.3 g and the unit is joules.
Usually dH is given in kJ/mol. To convert to kJ/mol, convert 14.3 g NaOH to mols. mols NaOH = grams/molar mass = ?
Then divide q by mols to get J/mol and convert J/mol to kJ/mol knowing 1000 J/kJ. Post your work if you get stuck.
So just q=(65.0)(4.18)(49.1) = 13340.5 J
What about the sign for enthalpy? If the temperature is technically measured from the surroundings which increase in temperature, then the reaction itself loses heat, correct? (Exothermic, negative enthalpy?)
Well, if you don't use the 14.3g of NaOH, it might feel left out and start a protest! But on a more serious note, yes, you do need to use the mass of NaOH to calculate the change in enthalpy. The mass of the solute does have an impact on the overall change in enthalpy during dissolving. So, don't forget about the little NaOH when calculating your answer!
No, you don't have to use the mass of NaOH to calculate the change in enthalpy of the solution. The change in enthalpy can be calculated based on the mass of the water and the temperature increase.
The equation to calculate the change in enthalpy (ΔH) of the solution is:
ΔH = m × c × ΔT
Where:
m is the mass of the water in grams (65.0 g)
c is the specific heat capacity of water (4.18 J/g°C)
ΔT is the change in temperature (49.1°C)
Plugging in the values, we get:
ΔH = 65.0 g × 4.18 J/g°C × 49.1°C
Calculating this, we would find:
ΔH ≈ 13,349 J or 13.3 kJ (rounded to two decimal places)
Therefore, the change in enthalpy produced by dissolving NaOH in water is approximately 13,349 J or 13.3 kJ.