help with chemical change

Question

I am suppose to pick the possible answers that show examples of chemical change in matter

 

a.  burning wood until it becomes ashes

b.  combining nitrogen and oxygen gases to make ammonia (NH₃₎

c.  adding baking soda to flour and water to make bubble so that bread will rise

d.  all of these

 

I know  that physical change is the result of a new set of condition imposed on the same material but I cannot figure out how to tell if these are chemical changes

 

thanks

Answer 1

The easy way to think about a chemical change is this:

If a molecule, different than any of the starting molecules, appears as a result of the change, it is a chemical change.   In other words, chemical changes make new molecules.   So in burning wood, carbon dioxide and water are produced;  the NH3 molecule was not present before the change;  bread rises because CO2 gas is produced in a change.    All three example are chemical changes.