A substance undergoes change. Which Of the following indicates that the change was a chemical change?

a. the substance changed state.

b. the molecules of the substance changed

c. the substance changed shape.

d. the density of the substance changed.

The study of matter and energy is

How do you use the periodic table to find the matter, number of subatomic particles, family name, reactivity, and number of valence electrons?

Consider the group 1a elements sodium (period3), potassium (period 4) and rubidium period 5). whatwould you predict about the ionization energies of theses elements?

When 1.187 g of a metallic oxide is reduced with excess hydrogen 1.054 g of the metal is produced. what is the metallic oxide?

Which bond is most polar C-O, H-O, N-O, S-O

What is the rough er connected to

Two students design an experiment to see if pushing or pulling a box across the floor is more effective. The first student pushes the box across the floor a distance of 20 feet and the second student times how long it takes.

15.00 g of NH4HS (s) is introduced into a 500. mL flask at 25 °C, the flask is sealed, and the system is allowed to reach equilibrium. What is the partial pressure of ammonia in this flask if Kp = 0.108 at 25 °C for: NH4HS (s) ⇄ NH3 (g) + H2S (g) ?

Among elements 1-18, which element or elements have the smallest effective nuclear charge if we use the equation zeff=z-s to calculate zeff? check all that apply.

Two clear solutions are placed in separate beakers. The first solution has a pH of 4, and the pH of the second solution is unknown. If the two solutions are mixed and the resulting pH is 5, the second solution must have