What element has 21 neutrons, 20 electrons and 20 protons

The change in entropy, Δ S ∘ rxn, is related to the the change in the number of moles of gas molecules, Δ n gas.

15 grams of NaCl are added to a beaker. It is dissolved in 200 ml of water and diluted up to 250 ml. What is the Na + concentration in moles/liter in the final solution? (Atomic mass are Na = 22.99 g/mole, Cl=35.45 g/mol)

J. Explain how an atom's valence electron configuration determines its place on the periodic table.

How can you drop two eggs the fewest amount of times, without them breaking?

A 133.8-gram sample of bronze was 10.3% tin by mass. Determine the total mass of tin in the sample.

What is the definition of Amplitude?

An excess of NiCO3, 12 g, was added to 40cm cube of sulpheric acid, 2.0 mol/dm cube. The unreacted nickel carbonate was filtered out and the filtrate evaporated to optain the crystals.

Under what condition is decompostion the fastest? Under what condition is it the slowest?

Which compound has the strongest hydrogen bonding between its molecules? 1. HBr 2. HF 3. HCl 4. HI

Arrange the following bonds in order of increasing polarity: O-H, C-H, F-H, H-H A) O-H B) C-H<0-H C) H-H D) C-H E) HH