A calorimeter contains 34.0 mL of water at 12.0 C . When 2.20 g of X (a substanc
ID: 898266 • Letter: A
Question
A calorimeter contains 34.0 mL of water at 12.0 C . When 2.20 g of X (a substance with a molar mass of 63.0 g/mol ) is added, it dissolves via the reaction
X(s)+H2O(l)X(aq)
and the temperature of the solution increases to 26.5 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
q=mct
where q is the change in energy(delta h),
t is the change in temperature
c is the specific heat of water,
and m is the total mass of the solution. the density of water is ~1g /ml.
q = (36.2) x (4.18) x (14.5)
q = 2194.082 J
you then find the number of moles of X. the formula is
mass of x / molar mass of x = number of moles
if we know molar mass of X we can find the change per mole. but molar mass not provided
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