Which of these indicate that a chemical reaction has occurred?

A.) Formation of a gas.

B.) Boiling of a substance.

C.) Melting of a substance.

D.) Freezing of a substance.

In an acid/base lab, a student used blue litmus paper and placed it in the sample. It stayed blue. Then the student used red litmus paper and it stayed red. What should the student's conclusion be?

The enthalpies of formation of the compounds in the combustion of methane, CH4 (9) + 20, (g) → C02 (g) + 2H2O (g), are CH4 (g) : AH = - 74.6 kJ/mol; CO2 (g) : AH + = - 393.5 kJ/mol; and H2O (g) : AHp = - 241.82 kJ/mol.

You have four bottles labeled 1, 2, 3, 4. Each bottle has a white powder in it. The identities of the substances are held secret by the teacher. Mr. Sandstone wants you to try and experiment with the substances to figure out what they are.

What is the nature of this chlorine ion?

Silicon has some properties of metal and some properties of non metals silicon is used on solar panels.

An analytical chemist is titrating 242.5 mL of a 1.200 M solution of hydrazoic acid HN3 with a 0.3400 M solution of NaOH. The pKa of hydrazoic acid is 4.72. Calculate the pH of the acid solution after the chemist has added 1006.

A gas stream contains 18.0 mol% hexane and the remainder nitrogen. the stream flows to a condenser, where its temperature is reduced and some of the hexane is liquefied. the hexane mole fraction in the gas stream leaving the condenser is 0.0500.

What type of solution is aerated water. why is it so.

What elements form chemical bonds

Which of the following is not a pseudoscientific claim