if a 3.5g of solid of NaOH is added to 165 mL of H2O and temprature change 4.2 C. find molar enthalpy of NaOH?

Question

specific heat capacity of water is 4.18 J/g*C, molar mass of NaOH is 40 g/mol, molar mass of water is 18 g/mol
the formula for molar enthapy is Q/mol.
the formula for Q is mass* change in temp*specific heat capacity.

plzzz help me out with this question asap...thankx

Answer 1

OK, I am here to your rescue.
Normally I dislike these kind of questions: a lot of rough approximations are involved without specifically clear statement.
Approximate One: No heat loss is considered.
Approximate Two: Heat capacity of 3.5g NaOH is not considered.
Approximate Three: Volume change is ignored.
Approximate Four: Water temperature is not given, thus let the density to be 1g/ml.
Now...
3.5g of solid of NaOH added to 165 mL of H2O, release heat of:
(4.18 J/g*C)*(165 mL *1g/mL)*4.2 C = 2.90 kJ
Hence the molar enthapy is:
(2.90 kJ)*(40 g/mol)/(3.5g ) = 33.1 kJ/mol

Answer 2

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