When two substances are mixed and light is produced is it a chemical or physical change?

What is the porcent of H in NH3

Predict the reactants of this chemical reaction. That is, fill in the left side of the chemical equation. Note: you are writing the molecular, and not the net ionic equation. → CaCl2 (aq) + H20 (l)

You started with 64 g of a radioactive substance. If you have 4.0 g of that substance left, then how many half-lives have elapsed? a. 2 b. 3 c. 4 d. 5

Explain why one spark will ignite propane gas and no more sparks are needed for the propane gas to continue burning.

When chemical x is added to a certain liquid, it breaks down into chemicals y and z. it is not possible to simplify chemicals y and z more. why are chemicals y and z elements?

How many moles of h2so4 are required to react with 6.80 miles of al2o3

Which explanation best describes a wave? A. a disturbance that travels through a medium with a transfer of energy and matter B. a disturbance that travels through a medium without a transfer of energy and matter C.

The requirements for one type of atom to substitute for another in a solid solution are:

How could you separate items that are different densities? explain

Why do elements within a period of the periodic table have different properties