Look at the picture of the equation provided. Which of the following indicates that a chemical reaction may be present? (CHECK STATES OF MATTER)

A student heated a 10 gram sample of a chemical in an open container. A chemical reaction occurred, and the mass of the sample was measured again. The mass of the sample was found to be less than before the reaction. Which of the following best explains the decrease in mass of the sample?

Which of the models of a chemical reaction best represents the Law of Conservation of Mass?

What type of reaction is the following: $$2NaHCO_3->\ Na_2CO_3+CO_2+H_2O$$  

What type of reaction is the following: $$BaCl_2+2KI\ ->\ 2KCl\ +\ BaI_2$$  

What are the coefficients that will balance the skeleton equation below?

__MgS + __O₂ → __MgO + __SO₂

What are the coefficients that will balance the skeleton equation below?

__Na + __F₂ → __NaF