Explain how to separate a mixture of sand and pebbles.

List four observations that indicate that a chemical reaction may be taking place

Before it was launched, a helium-filled balloon had a pressure of 201 kpa at a temperature of 27°c. at an altitude of 15,000 m, the pressure had decreased to 2.5 kpa and the temperature had dropped to -14 °c. the volume of the balloon increased to 59.3 m3. what is the original volume of the balloon? 13 m3 0.85 m3 0.077 m3 1.17 m3

How much energy is required to vaporize 2 kg of copper? a 4730 kj b 207kj c 9460 kj d 414kj