How many calories of energy (heat) is released when 250.0 g of lead is cooled from 15.0˚C to 12.0˚C.

Tin has ten stable isotopes. the heaviest, 124sn, makes up 5.80% of naturally occuring tin atoms. how many atoms of 124sn are present in 82.0 g of naturally occurring tin? what is the total mass of the 124sn atoms in this sample?

If i can still dissolve more sugar into the solution at a certain temperature what would i call that solution

Which class of molecules functions as chemical signals? hormones water carbohydrates proteins