Changing a chemical property of a substance never alters its chemical composition.
always alters its chemical composition.
will only alter its chemical composition if the change is small.
will only alter its chemical composition if the change is large.

A chemical change in a substances always alters the chemical composition.

Explanation:

Molecules always are combined to create a new substance, otherwise it would only be a physical change and the substance would have still had the same molecular design.

petroleum? coal maybe?

"standard molar enthalpy:

h2o ( liquid water ) : - 285.8 kj/mole

h2o ( water vapor ) : - 241.8 kj / mole.

δhrxn = - 241. 8 - ( - 285.8 )= -241.8 + 285.8 = 44.0

answer: 44.0 kj"