Here's a rough explanation of BLK 33's question (mech engineer's idea of a chemical engineering question, so numbers aren't exact). Any chemical engineer's out there are quite welcome to correct me if I'm wrong.
For 'complete' combustion of 140 tonnes of Jet-A1 you need to stuff about 1,600 tonnes of air into the core engine (bypass air is another story). Total into the engine 1,740 tonnes.
Out of the tailpipe you'll get about 420 tonnes of CO2, 100 tonnes of water, and 1,220 tonnes of nitrogen. Total out of engine 1,740 tonnes.
The 140 tonnes of Jet-A1 contained about 80 tonnes of C, so with 340 tonnes of O2 from the air, we have 420 tonnes of CO2.
About 7 tonnes of H2 in the Jet-A1 combined with more O2 from the air gives us the 100 tonnes of water. That's where the contrail comes from.
Both CO and NOX are products of inefficient combustion, so should only be there in small amounts (measured in parts per million).
Not sure about the black exhaust of the 777. It would be soot from really poor, incomplete combustion. Haven't noticed it much since the days of early 707's and DC-8's