Question

1) You place a 50mL of 0.50M NaOh and 25mL of 0.50M HCl in a coffee cup calorimeter. What is the final temperature of the calorimeter if the initial temperature of the solution is 15.8 degree celsius. ( The change in enthalpy for the reaction is -55.4 kJ/mole H2O) (assume the solution has specific heat and density as water, s=4.184 J/g oC, density=1.00 g/L)

2) It took 3.20 min for 1.00 L N2 to effuse through a porous barrier. How long will it take for 1.00L of Cl2 to effuse under the same condition?

Answer 1

1) no of mole of HCl reacted = 25*0.5 = 12.5 mmole = 0.125 mole

no of mole of NaOH = 50*0.5 = 25 mmole = 0.25 mole

amount of heat released(q) = DHrxn*n = -55.4*0.125 = -6.925 kj

amount of heat released(q) = m*s*DT

mass of solution = d*v = 1*(50+25) = 75 g

   6.925*10^3 = 75*4.184*(x-15.8)

x = final temperature = 37.9 c

2) r1/r2 = sqrt(M2/M1)

rate of diffusion of N2(r1) = 1/3.2 = 0.3125 l/min

M1 = 28 g/mol

r2 = rate of diffusion of Cl2 = ?

M2 = 71 g/mol

0.3125/r2 = sqrt(71/28)

r2 = rate of diffusion of Cl2 = 0.196 l/min

time required for cl2 = amount / rate = 1/0.196 = 5.1 min