MasteringChemistry: MC09-Google Chrome chemistry.com/myct/itemView?assignmentPro
ID: 1040219 • Letter: M
Question
MasteringChemistry: MC09-Google Chrome chemistry.com/myct/itemView?assignmentProblemiID-973774298offset-next C2017 > Part A n which a easuring the alculate the e reaction using A calorimeter contains 30 0 mL of water at 120-c when 2.30 g of X (a substance with a molar mass of 780 g/mol) is added, it dissolves via the reaction and the temperature of the solution increases to 250C Calculate the enthalpy change AH, for this reaction per mole of X Assume that the specific heat of the res trg solution is equal to that of water 418J/k-ci mined heat that density of water is 1.00 g/mL and that no heat is lost to the calorimeter itself, nor to the change for the g, that is Express the change in enthalpy in kilojoules per mole to three significant figures View Available Hint(s) of reactant and the ergy change, AE s the sum of kJ/mo with a bomb Part B 657 PM MacBook Pro 5 6 8 0Explanation / Answer
Mass of reactant= 2.30 g
So, moles of reactant = mass / molar mass
= (2.30 g) / (78 g/mol)
= 0.0295 mol
Mass of solution (m ) = 30 g
Initial temperature, T1 = 12.0 oC
Final temperature, T2 = 25.0 oC
Change in temperature, ?T = T2- T1
= (25.0 oC – 12.0 oC)
= 13.0 oC
Specific heat capacity of water Cp = 4.184 J g-1oC-1
Heat generated,
Q = m x Cp x ?T ……….. (1)
or, Q = (30 g) x (4.184 J g-1oC-1) x (13.0 oC)
or, Q = 1631.76 J
or, Q = 1.63 kJ
Now, Change in enthalpy
?H = Q / number of moles
?H = 1.63 kJ / 0.0295 mol
?H = 55.25 kJ/ mol
?H = 55.3 kJ/ mol
This reaction is producing energy so it a exothermic reaction
And in exothermic reaction ?H is always negative
So our answer will ?H = - 55.3 kJ/ mol
image 2:
The heat produced in a bomb calorimeter when combusting a given amount of known substance is the internal energy of the substance combusted per the number of moles of the substance that was burned.
Mass of sucrose = 10.0 g
Molar mass of sucrose = 342.3 g/mol
So, moles of sucrose = (10.0 g) / (342.3 g/mol)
= 0.02921 mol
You are given that the heat capacity of the calorimeter is 7.50 kJ oC-1. This means that the temperature of calorimeter increases 1 oC when 7.50 kJ of heat is absorbed by the calorimeter from the combustion process. Since the temperature increase was 22.0 oC when combusting the 0.02921 moles of sucrose, then the combustion process must have given off (22.0 oC) x (7.50 kJ oC-1) = 165.0 kJ.
Therefore, the change in internal energy per mole of sucrose combusted would be = (165.0 kJ) / (0.02921 moles of sucrose combusted) = 5649 kJ/mol of sucrose combusted
Because the surroundings gained energy, we know that the system released energy and the sign of the change in internal energy must be negative. answer = -5649 kJ/mol = 5.65 x 103 kJ/mol