Chemistry Help!?

Question

Does heating copper sulfate produce a chemical or physical change? Why?

Also, does heating sucrose (table sugar) produce a chemical or physical change? Why?

Answer 1

A chemical change involves the breaking and making of chemical bonds. A physical change does not involve the making or breaking of chemical bonds but involves a change in physical properties. So the argument revolves around 'what is a chemical bond?'

Some people might argue that the thermal decomposition of hydrated copper(II) sulphate does not involve the breaking of chemical bonds because the water molecules which are formed were only attached to the copper ions by relatively weak electrostatic forces which cannot be described as bonds - consequently it is a physical change.

Others might argue that the water is chemically bonded to the copper(II) ions in hydrated copper sulphate and it is therefore a chemical change.

There is no hard and fast distinction between a chemical bond and an attractive force between particles so the jury will always be out on this one.

In my personal opinion the reaction below does involve a chemical change:

CuSO4.5H2O --> CuSO4 + 5H2O

There is no such doubt about your second example. Lots of bonds are broken and made so it is definitely a chemical change.

Answer 2

Heating hydrated copper (ll) sulpahte is a physical change as no new compounds are formed (the compounds water and copper (ll) sulphate are seperate compouds). The products of heating are white anhydrous copper (ll) sulphate and water. This process is easily reversed physically be adding the water back to the white anhydrous copper (ll) sulphate.
Physical changes are usually easily reversable, while chemical changes are not so easily reversed.
However, heating table sugar would produce new compounds as the sugar undergoes thermal decomposition. This is a chemical change was new products are formed.
This change is not easily reversed (try to convert the carbon residue back to sugar!)

Answer 3

These both produce new chemicals. The first produces white anhydrous copper sulphate, and the second produces brown caramel and then black carbon.