Question

1- Explain the concept of density in gases; why does SF6 cause one’s voice to appear deeper? (kindly provide a bit detail )

2- Calculate the internal energy change in a process that performs 855 J of work on the system and produces 1422 J of heat released to the surroundings. (answer: 567 j)

3- 52.81 g of a gas occupy 30.4 L of volume at 729.6 torr and 23.0 ˚C. What is the molecular weight of the gas? What density does it exhibit at STP? (answer: 44.0 g/mol; density at STP= 1.96 G/L)

4- To 100.0 mL of a 1.10 M HCl solution in a calorimeter at 22.35°C are added 0.110 moles of sodium hydroxide, and the temperature rises to 37.59°C, what is the molar enthalpy of reaction for this reaction, assuming the density and specific heat of the solution are the same as that of water, and assuming a perfectly insulating calorimeter (no heat loss from solution)? (answer: -58.0 kj/mol)

Answer 1

2) from first law of thermodynamics

du = q+w

       = 855-1422
  
       = -567 j

-ve sign indicates energy released.

3) from ideal gas equation

   PV = nRT

   Pv = (w/mwt)RT

   (729.6/760)30.4 = (52.81/X)*0.0821*300

X = molarmass of gas = 44.6 g/mol

density of gas = P*Mwt/RT

                = (729.6/760)*44.6/(0.0821*273.15)

                 = 1.91 g/L

4)
   no of mole of HCl Taken = 100*1.1/1000 = 0.11

   no of mole of NaOH added = 0.11

heat released(q) = m*s*DT

     m= mass of solution = 100 ml *1 g/ml = 100 g

      s = specific heat = 4.184 j/g.c

      DT = 37.59-22.35 = 15.24 c

   q = 100*4.184*15.24

     = 6.376 kj

   molarenthalpy (DH) = -q/n = -6.376/0.11   = -58 kj/mol