In a constant pressure calorimeter at standard conditions, 0.400 mol sodium meta
ID: 894981 • Letter: I
Question
In a constant pressure calorimeter at standard conditions, 0.400 mol sodium metal is reacted with 432.0mL of water as indicated in the following balanced equation:
The dry calorimeter apparatus has a total heat capacity of 678 J/C
The calorimiter, water and sodium metal all have an initial temperature of 25.20C and a final temperature of 34.20C
The aqueous solution that results has a total volume of 401.0 mL and a density of 1.04 g/mL
The aqueous solution has the same specific heat as pure water: 4.184 J/g*K
The calorimeter is perfectley insulated
Hint: Na is the limiting reactant
Explanation / Answer
Heat given out by reaction has raised the temperature of calorimeter and aqueous solution.
mass of water, mw = density * volume
= 1.04 g/mL * 401 mL
= 417.04 g
Q = Nc*(Tf-Ti) + mw*Cw*(Tf-Ti)
= 678 * (34.2-25.2) + 417.04*4.184*(34.2-25.2)
=21806 J
= 21.81 KJ
0.4 mol Na gives 21.81 KJ of heat.
In reaction coefficient of Na =2
So, 2 mol will give : 21.81*2/0.4 = 109.1 KJ
deltar H = qp
so,.
delta H of reaction =109.1 KJ
To find delta U use:
delta H = delta U + ng*R*T
ng = numbe of moles of gases = 1 mol (2 mol of Na gives 1 mol of H2)
T = 34.2 oC = (34.2 + 273) K = 307.2 K
delta H = delta U + ng*R*T
109100 J = delta U + 1*8.314*307.2
delta U = 106500 J
= 106.5 KJ