Why do sidewalks have built-in cracks every few feet

Water (2510 g ) is heated until it just begins to boil. if the water absorbs 5.09×105 j of heat in the process, what was the initial temperature of the water?

Asample of ammonia reacts with oxygen as shown. 4nh3(g) + 5o2(g) 4no(g) + 6h2o(g) what is the limiting reactant if 4.0 g of nh3 react with 8.0 g of oxygen? o2 because it produces only 0.20 mol of no. nh3 because it produces only 0.20 mol of no. o2 because it produces two times less no than nh3. nh3 because it produces three times more no than o2.

How can carbon move from "land" to bodies of water? describe the way human impact has lead to increased levels of co2 in the atmosphere.