Part A: What is the balanced chemical equation for the reaction used to calculat
ID: 1025054 • Letter: P
Question
Part A: What is the balanced chemical equation for the reaction used to calculate Hf of CaCO3(s)? Express your answer as a chemical equation.
Part B: A calorimeter contains 35.0 mL of water at 15.0 C . When 2.40 g of X (a substance with a molar mass of 57.0 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.
Part C: Consider the reaction C12H22O11(s)+12O2(g)12CO2(g)+11H2O(l) in which 10.0 g of sucrose, C12H22O11, was burned in a bomb calorimeter with a heat capacity of 7.50 kJ/C. The temperature increase inside the calorimeter was found to be 22.0 C. Calculate the change in internal energy, E, for this reaction per mole of sucrose. Express the change in internal energy in kilojoules per mole to three significant figures.
Explanation / Answer
1. Ca(s)+C (s)+3/2O2 (g)------>CaCO3(s) is used for calculating the deltaHo for CaCO3 sinnce standard heats of formation of all elements in their standard state =0
2. mass of water= volume of water* density = 35 ml* 1g/ml= 35 gm, mass of sample = 2.4 gm
total mass of solution = mass of water+ mass of sample =35+2.4= 37.4 gm
specific heat of solution is considered same as that of water= 4.184 j/gm.deg.c
hence enthalpy change = -mass of sample* specific heat* change in temperature = -37.4*4.184*30=-4694 joules
this is enthalpy change when 2.4 gm of sample of molar mass= 57 g/mole is dissolved.
moles of sample = mass/ molar mass= 2.4/57
enthalpy change/mole = -4694*57/2.4 joules/mole =-111483 joules/mole= -111.48 Kj/mole
2 enthalpy change=- heat capacity of calorimeter* change in temperature==7.5*22 Kj ( since there is an increase in temperature, the reaction is exothermic and enthalpy change is -ve)=-165 Kj
H= U+PV
deltaH= deltaU+deltan*RT
where ,deltan= change in number of moels of gaseous products formed during the reaction =12-12= 0
deltaH= deltaU= -165 Kj
mass of sucrose= 10gm, molar mass of sucrose (C12H22O11)= 12*12+22*1+16*11= 342 g/mole
moles of sucrose = mass/molar mass = 10/342 moles= 0.029 moles
enthallpy change per moles = -165/0.029 Kj/mole= -5690 Kj/mole