18) The standard enthalpy of vaporization of carbon tetrachloride, CCl, at its b

Question

18) The standard enthalpy of vaporization of carbon tetrachloride, CCl, at its boiling point of 349.9 K is AH vap +30.00 kJ/mol. What enthalpy change of the system is required to convert 10.00 g of CCla gas to a liquid at 349.9 K? (CCl4 molar mass 153.82 g/mol) A. -857.4 J B. -1.950 kJ C. +461.5 k.J D. +300.0 k.J E. -461.5. k.J 19) The specific heat capacity of NaOH(s) is 1.498 J/(g.C). Calculate the enthalpy change associated with changing the temperature of 150.0 g of NaOH from 75.0 °C to -25.0 °C. A. +22.47 kJ B. -5.618 J C. -83.85 kJ D. 0.9987J E. -22.47 k.J 50 20) Which one of the following reactions occurring at 25°C and 1 atm pressure corresponds to the reaction associated with the standard enthalpy of formation of sodium carbonate, NaHCO (s)? A. NaHCOs(s) -Na (a)+ HCOs (aq) B. NaHCOs(s) - Nag)+ 1/2 H:(g) + C(diamond) +3/2 01(g) C. Nag) +Hg) C(e) +3 0.(g) NaHCOs(s) D. Na(s) 1/2 H2(g) + C(graphite) +3/2 02g)NalHCOs(s) E. Na(s) 1/2 H(g) + C(diamond) + 3/2 02(g)- NaHCOs(s)

Explanation / Answer

Ans 8

Enthalpy of vaporization = 30 kJ/mol

Mass of CCl4 = 10 g

Moles = mass/molecular weight

= 10g / 153.82 g/mol

= 0.065 mol

Enthalpy change at phase change from gas to liquid

= - 30 kJ/mol x 0.065 mol

= - 1.950 kJ

Option B is the correct answer

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