Hydrogen and fluorine react together in the following way: H, +F, → 2HF. The overall energy change of the reaction is -542 kJ/mol.
The H-H bond energy is 436 kJ/mol and the F-F bond energy is 158 kJ/mol.
Grade
7-9
Calculate the energy of the H-F bond.
goed
our
-
Oro
bu
k/mol
H-F bond energy
Total 3 marks)
multiplication

Astudent is given a sample of a blue copper sulfate hydrate. he weighs the sample in a dry covered porcelain crucible and got a mass of 23.875 g for the crucible, lid, and sample. the mass of the empty crucible and lid was found earlier to be 22.652 g. he then heats the crucible to expel the water of hydration, keeping the crucible at red heat for 10 minutes with the lid slightly ajar. on colling, he finds the mass of crucible, lid, and contents to be 23.403 g. the sample was changed in the process to very light clue anhydrous cuso4. if there are again 100.0 g of hydrate, how many grams of cuso4 are in it? how many moles of cuso4? (hint: molar mass of cuso4 = 159.6 g / mole. what per cent of the hydrate is cuso4? you may convert the mass of cuso4 to moles.)

1. list three scientific reasons cockroaches may fly.

What are the similarities of physical and chemical change ?