1. butane has a chemical formula ch4h10. the equation 2c4h10 + 13o2 → 8co2 + 10h2o represents which of these?
a) a physical change of butane into other substances.
b) a chemical change of butane into other substances.
c) a physical change of other substances into butane.
d) a chemical change of other substances into butane.
2. an atom is analyzed in terms of its energy levels.

when a hydrogen atom absorbs a photon, and an electron moves from energy level 1 to level 2, what happens to the energy of the atom?
a) it increases.
b) it decreases.
c) it remains the same.
d) it increases and then decreases.
3. the initial pressure exerted on 1.0 liter of gas is 100 kpa. the pressure is changed and the new volume of gas is 0.25 liters. the pressure is changed to
a) 25 kpa.
b) 200 kpa.
c) 400 kpa.
d) 4000 kpa.
4.all but one of these compounds is a base. that is
a) nh3.
b) naoh.
c) hclo4.
d) nh4oh.
5.
consider the reaction mechanism,

a + o3(g) → b + o2(g)
c + o(g) → d + o2(g)

if a catalyst were used in the reaction mechanism, where would it likely appear?
a) a and b
b) c and d
c) b and c
d) a and d
6. the melting and boiling points of the hydrides of the elements of a group increase with increasing molecular weight. then why is hydrogen sulfide (h2s) a gas, but water (h2o) is a liquid?
a) h2s is acidic in nature
b) h2s has higher molecular weight
c) h2s has stronger intermolecular force of attraction
d) h2o has stronger intermolecular force of attraction

1) Answer is: B) A chemical change of butane into other substances.

Balanced chemical reaction: 2C₄H₁₀ + 13O₂ → 8CO₂ + 10H₂O.

This is chemical change (chemical reaction), because two new substances are formed (carbon dioxide and waters), the atoms are rearranged and the reaction is followed by an energy change.

This is not physical change, because the same substance is present before and after the psysical change, just with different form or state of matter.

2) Answer is: A) It increases.

Electrons can jump from one energy level to another, absorbing or emitting electromagnetic radiation with a frequency ν (energy difference of the levels).

Albert Einstein (1879-1955) proposed that a beam of light is a collection of discrete wave packets (photons) with energy hν, where h is Planck constant and ν is frequency.

Energy level 2 has higher energy than energy level 1.

3) Answer is: C) 400 kPa.

Boyle's Law (the pressure-volume law): volume of a given amount of gas held at constant temperature varies inversely with the applied pressure when the temperature and mass are constant.  

p₁V₁ = p₂V₂ (the product of the initial volume and pressure is equal to the product of the volume and pressure after a change).  

p₁ = 100 kPa; starting pressure.  

V₁ = 1.0 L., starting volume.

V₂ = 0.25 L; final volume, smaller than starting volume.

p₂ = ?; final pressure.  

100 kPa · 1 L = p₂ · 0.25 L.  

p₂ = 100 kPa · 1 L / 0.25 L.  

p₂ = 400 kPa.  

When volume goes up, pressure goes down.  

When volume goes down, pressure goes up.  

4) Answer is: C) HClO₄.

Balanced chemical reaction of dissociation of perchloric acid in water:

HClO₄(aq) → H⁺(aq) + ClO₄⁻(aq).

Ionic compounds (in this example perchloric acid) conduct electricity, because it dissociate in ions and ions conduct electicity.  

Ionic substances dissociate in water on cations and anions.  

Perchloric acid (HCO₄) is one of strongest inorganic acids.  

NH₃ is ammonia, NaOH is sodium hydroxide and NH₄OH ammonium hydroxide, all are bases.

5) Answer is: D) A and D.

A catalyst is a chemical species that is present at the beginning of a reaction and reappears at the end.

An intermediate forms during the reaction and disappears before the end.

Catalysis is the increase in the rate of a chemical reaction due to the participation of an additional substance called a catalyst.

Reactions occur faster with a catalyst because they require less activation energy.

6) Answer is: D) H2O has stronger intermolecular force of attraction.

Intermolecular forces are the forces between molecules or particles.

Because of hydrogen bonds, water has higher melting and boiling temperatures than H₂S.

In molecule of water there are dipole-dipole forces between negatively charged oxygen from one molecule of water and positively charger hydrogen of another molecule of water.

Hydrogen bond is an electrostatic attraction between two polar groups that occurs when a hydrogen atom (H), covalently bound to a highly electronegative atom such as flourine (F), oxygen (O) and nitrogen (N) atoms.