1. What is the greenhouse effect? Explain why the coldest temperatures in winter always occur on clear nights. (7%)

2. The reaction of ethane gas (C2H6) with chlorine gas produces C2H5Cl as its main product (along with HCl) and a variety of other minor products. Calculate the percent yield of C2H5Cl if the reaction of 300. g of ethane with 650. g of chlorine produced 490. g of C2H5Cl. (atomic mass: C, 12.01； Cl, 35.45； H, 1.008) (8%)