Question

A calorimeter contains 30.0 mL of water at 12.5 ∘C . When 2.20 g of X (a substance with a molar mass of 82.0 g/mol ) is added, it dissolves via the reaction X(s)+H2O(l)→X(aq) and the temperature of the solution increases to 25.5 ∘C . Calculate the enthalpy change, ΔH, for this reaction per mole of X. Assume that the specific heat of the resulting solution is equal to that of water [4.18 J/(g⋅∘C)], that density of water is 1.00 g/mL, and that no heat is lost to the calorimeter itself, nor to the surroundings

Answer 1

-67384.61 joule/mole is the enthalpy change.

Explanation:

Data given:

mass of water = 30 ml

initial temperature = 12.5 degrees

final temperature = 25.5 degrees

mass of substance = 2.20 grams

q =?

c of water = 4.186 j/g C

number of moles of substance X = $\frac{2.2}{82}$

                           Number of moles = $\frac{mass}{atomic mass}$

   number of moles = 0.026 moles

formula used,

q = mc ΔT

q = (30 + 2.20) 4.186 x 13

  = 1752 J is the energy absorbed by water.

Heat released in the reaction is -1752 joules

Change in enthalpy ΔH = $\frac{energy released}{number of moles}$

putting the values:

$\frac{-1752}{0.026}$

= -67384.61 joule/mole