Which describes the reaction of a substance to form one or more new substances? a. a physical change b. a change of state c. a chemical change

A change of state just means it goes into a gas or a liquid or a solid from a liquid gas or solid. It change of state is going from one state to another. A change of state is not the answer.

A physical change can mean something as simple as a change in temperature or a change of state or dissolving in (say) water (like sugar and water). This is not your answer either.

The actual answer is a chemical change. Whenever there is a chemical change, bonds are broken and when that happens, something new is formed. So C is the answer.

1. 1 mole of anything contains 6.022x10^23 pieces  

d  

2. a  

3. c, number  

5. 1.24x10^24atoms / 6.022x10^23atoms/mole = 2moles h2 atoms  

6. fe2br3 mass = 2moles x mass fe + 3 moles x mass br  

molar mass = grams / number of moles = g/mole  

to find moles = g / molar mass  

to find mass = g = molar mass / moles