How would i do this chemistry question?

Question

For the following reaction to occur


MgSO4 → Mg2+(aq) + SO42−(aq)


the change in enthalpy must be −91.3 kJ/mol


How much heat (kJ) is lost or gained by 253.0 ml of water when 3.60 g of MgSO4 is dissolved in the water ?

*** you dont get that by multiplying what philippe said though. how do you figure thats the answer?

THANK YOU!!!!!! but i also need to know what the Change in temperature of the above process is. please help?

Answer 1

The mole of MgSO4 = 3.6/ (24+32+4*16) = 0.03 moles

MgSO4 --> Mg2+ + SO4 2- delta H = -91.3 kJ/mol

1 mole gives out -91.3 kJ
0.03 mole of MgSO4 would give = 0.03/1 * 91.3
= 2.739 kJ of heat

Answer 2

1. Convert 3.60 g of MgSO4 into moles using 120.4 g/mol for molecular weight.

2. Multiply the answer from #1 (.03 mole) by -91.3kJ/mol. The answer is -2.71x10^-2 kJ. Heat was lost since the change in enthalpy is negative.