Question

1. Calcium carbide(CaC2) reacts with water to form acetylene (C2H2) and Ca(OH)2

H degree = -127.2 kj

How much energy is released when 52g of C2H2 is formed in the reaction?

2. Elements from which of the following groups have a valence electron shell configuration ns^2np^5

A) noble gases

B)halogens

C) alkali metals

D) chalcogens

Answer 1

the reaction is CaC2+2H2O ----->Ca(OH)2+C2H2 is the balanced reaction

1 mole of CaC2 released 127.2 KJ of heat energy ( the reaction releases heat as seen by the sign of enthalpy change)

mole= mass/ molar mass, molar mass of C2H2= 24+2= 26 g/mole

26 gm of C2C2 released 127.2 Kj of energy

52 gm of CaC2 releases 127.2*52/26= 254.4 KJ of energy

2. The electonic configuration suggests the elements will have a tendency to accept one electrons to fill the criteria ofr octet rule of 8 electons in the outermost orbit. This is the case with halognes. ( Hence B is correct)