What is the sign of the entropy change for the following reactions? Explain your answer.

a$.CaC{O}_3(s)C{O}_2(g)+$CaO$(s)$

b$.C_4{H}_8(g)+6O_2(g)4C{O}_2(g)+4H_{2}O(g)$

Calculate $S$ for the following reactions, using standard entropy values from formula chart.

a$.N{H}_3(g)+HBr(g)N{H}_{4}Br(s)$

b$.2N{O}_2(g)2NO(g)+O_2(g)$