Which of the following is a physical change

A copper roof changing colors from orange to green

Sawing a piece of wood in half

Rust forming on an iron fence

Burning a piece of wood

Hydrazine (N2H4) and dinitrogen tetroxide (N2O4) form a self-igniting mixture that has been used as a rocket propellant. The reaction products are N2 and H2O. 1. Write a balanced chemical equation for this reaction. 2.

Which of the answer choices correctly predicts the charge that would be present on a magnesium (Mg) ion, as shown in the periodic table? 2+ 1+ 1- 2-

Name these covalent compounds: SO2, P2CL5 and N2O4

Determine the molar mass of an unknown monoprotic acid to two decimal places if 20.01 ml of a 0.098 m naoh solution were used to titrate 0.215 g of the unknown acid

Scientist noticed that the ozone layer was thinning. what was occuring at the same time

Although DNA evidence cannot be obtained from hair evidence without a root, which of the following can be obtained from hair evidence?

Carbon naturally occurs in two forms: diamond and graphite. Why do these two forms have very different properties?

How many moles of hydrogen are evolved when an excess of sodium metal is added to one mole of citric acid?

Write a net ionic equation for the reaction that occurs when barium sulfite (s) and excess hydrochloric acid (aq) are combined. Note: Sulfites follow the same solubility trends as sulfates.

A hydrate is a compound with water molecules incorporated into its crystal structure. In an experiment to find the percentage of water in the compound, the following data was recorded.