A calorimeter contains 20.0 mL of water at 11.5 C . When 2.30 g of X (a substanc

Question

A calorimeter contains 20.0 mL of water at 11.5 C . When 2.30 g of X (a substance with a molar mass of 43.0 g/mol ) is added, it dissolves via the reaction

X(s)+H2O(l)X(aq)

and the temperature of the solution increases to 30.0 C .

Calculate the enthalpy change, H, 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/(gC)], that density of water is 1.00 g/mL, and that no heat is lost to the calorimeter itself, nor to the surroundings.

Express the change in enthalpy in kilojoules per mole to three significant figures.

Explanation / Answer

V = 20 ml of WAter

T = 11.5C

m = 2.3 g of X

MW = 43

X + H2O --> Xaq

Tf = 30

a) dHRXN

Q = m*Cp*dT = (20+2.3)*(4.184*(30-11.5) = 99.7 J

mol = mass/MW = 2.3/43 = 0.0535

HRXN = Q/n = 99.7/0.0535 = 1863.9 J/mol

Hrxn = -1863.9 J/mol

its negative since it is exothermic reaction

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.