Final Exam

Question 1

What is chemistry?

Answer 1

The study of the structure and composition of matter that makes up living things and their environment.

Question 2

How do the intermolecular forces compare between solids, liquids, and gasses (hint: think about how tightly the particles are held together)

Answer 2

Gasses are freely moving and bouncing around, solids are packed together and vibrating in place, and liquids are close together so that they move slowly.

Question 3

What is the law of conservation of mass? What does this mean for chemical reactions?

Answer 3

The law of conservation of mass states that mass is neither created nor destroyed. This means that for chemical reactions the reactants and products should have the same amount of mass.

Question 4

What is the difference between a mixture and a compound?

Answer 4

A compound is chemically combined, a mixture is just physically mixed together.

Question 5

What is the difference between a chemical change and a physical change?

Answer 5

Chemical changes are those where one or more substances are combined to produce a new substance. Physical changes are those in which the shape, size, or state of the matter changes, but the substance is still essentially the same.

Question 6

What are positive and negative ions called?

Answer 6

Positive ions are called cations and negative ions are called anions.

Question 7

Describe our current understanding of an atom.

Answer 7

Bhor’s atom, made of protons and neutrons in the nucleus and the electrons make up energy levels on the outside of the nucleus; these are called electron clouds.

Question 8

How many protons and electrons does a fluorine ion have (F1-)

Answer 8

Protons:9 Electrons:10

Question 9

How many valence electrons does oxygen have? Carbon? Magnesium?

Answer 9

O: 6, C: 4, and Mg:2

Question 10

What are valence electrons? Why is it helpful to know how many valence electrons an atom has?

Answer 10

The number of electrons in an atom’s outer shell. They are important because they show which electrons are shared and taken away during a chemical reaction.

Question 11

What is electronegativity and how does it impact bonding?

Answer 11

A measure of the tendency of an atom to attract electrons (or electron density) towards itself. It determines how the shared electrons are distributed between the two atoms in a bond.

Question 12

What are the periodic trends for atomic radius? For electronegativity?

Answer 12

Atomic radius is the trend of size and it decreases across the periodic table, because more protons make the atom smaller, and it increases across the periodic table because there are more energy levels. Electronegativity is the trend based on the attraction of electrons, it decreases down the periodic table because there’s less attraction in the energy levels, and increases across the periodic table because of more nuclear charge and less energy levels.

Question 13

For ionic and covalent compounds, which has a higher melting point? Why?

Answer 13

Ionic compounds have a higher melting point because their bonds are stronger than covalent compounds.

Question 14

What does VSEPR stand for? What does it predict?

Answer 14

VSPER stands for valence shell electron repulsion theory, which predicts that electron pairs in the outermost level try to get as far apart from each other as possible.

Question 15

When is a bond a polar covalent bond?

Answer 15

When a covalent bond has opposite charges.

Question 16

What happens to electrons in an ionic bond? For a covalent bond?

Answer 16

In ionic bonds, the metal loses electrons to become a positively charged cation, whereas the nonmetal accepts those electrons to become a negatively charged anion. In covalent bonds the electrons are shared equally.

Question 17

What are the three types of intermolecular forces (IMFs)? Which is the strongest?

Answer 17

Dipole-dipole: Stronger force than LD, polar molecules.
London Dispersion Forces (LDF): Weak force, nonpolar.
Hydrogen Bonding: Strongest force, occurs with molecules that have an H-F, H-O, or H-N bond.

Question 18

If a molecule has stronger IMFs, what can we predict about the boiling point of the substance?

Answer 18

The boiling point of a substance is higher, if the molecule has a stronger IMF.

Question 19

Which are stronger, bonds between atoms within a molecule or attractive forces between molecules (IMFs)?

Answer 19

Bonds between atoms within a molecule are stronger than attractive forces between molecules.

Question 20

What is a mole? Why do scientists use moles of atoms/molecules instead of the number or atoms/molecules? What number does a mole represent?

Answer 20

A mole is a unit of measure, it is used to represent and acknowledge the big numbers that atoms and molecules can’t represent. The number moles represent is 6.02x10 to the 23rd.

Question 21

What are some signs that a chemical reaction has occurred?

Answer 21

Formation of a precipitate or gas, change in color, odor or temperature, light being produced or bubbles, something is burning.

Question 22

What is a precipitate?

Answer 22

A type of solid that forms from two or more liquids.

Question 23

How do you know if a chemical equation is balanced?

Answer 23

If the same type of element has the same amount of atoms on both sides.

Question 24

What is the limiting reactant?

Answer 24

The reactant that limits the chemical reaction from creating anymore products.

Question 25

What are the coefficients in a chemical equation? What do they represent? Example: 5 H2O

Answer 25

Shows the amount of compounds in a chemical equation.

Question 26

For the following reaction: 2N2 + O2 → 2N2O , If you start with 6 moles of N2 and 6 moles of O2, which is the limiting reactant?

Answer 26

N2 is the limiting reactant.

Question 27

For the reaction 4NH3 + 3O2 → 2N2 + 6H2O, what is the mole ratio of ammonia (NH3) to water (H2O)?

Answer 27

4:6

Question 28

What is a process that absorbs heat called? What about a process that releases heat?

Answer 28

The process that absorbs heat is called an endothermic reaction, and the process that releases heat is an exothermic reaction.

Question 29

What is the difference between temperature and heat?

Answer 29

Temperature is the energy of an object, heat is what is transferred from one object to another.

Question 30

The quantity of heat required to raise the temperature of one gram of a substance by one degree celsius is known as what?

Answer 30

Specific heat capacity

Question 31

Why is melting an endothermic process?

Answer 31

Melting is an endothermic process because it absorbs heat and temperature which is how things melt.

Question 32

Describe collision theory. What is required for a successful collision?

Answer 32

The collision theory states that a chemical reaction can only occur between particles when they collide. For a successful collision molecules must collide with each other with sufficient energy and proper orientation.

Question 33

What are some ways to speed up a chemical reaction? How does each method achieve the faster rate?

Answer 33

1. Raising the temperature; which increase the energy and speed
2. Using a catalyst; speeds up the reaction by pairing molecules together.
3. Increasing concentration; which causes more particles to move together.
   4.Reducing space; less room for reactions to happen which means particles will start having more collisions and will move faster.

Question 34

What is a catalyst? How does it work?

Answer 34

A catalyst is a way to speed up chemical reactions, it helps particles match up with each other easily.

Question 35

What is a solution? What is the solute? What is the solvent?

Answer 35

A solution is a mixture of two or more substances that contains a solute and solvent. The solute is the thing that dissolves into the solvent.

Question 36

What is the difference between a concentrated solution and a dilute solution?

Answer 36

A concentrated solution has a large amount of dissolved solute, a dilute solution has a small amount of dissolved solute.

Question 37

How do acids behave when placed in water?

Answer 37

They dissolve and release bubbles.

Question 38

What is the difference between a strong acid and a weak acid?

Answer 38

A strong acid dissolves fully and has a lower pH value, a weak acid does not dissolve fully and has a high pH value.

Question 39

What pH values are associated with acids? What pH values are associated with bases?

Answer 39

Weak acids have higher pH values than strong acids, but strong bases have higher pH values than weak bases.

Question 40

What does it mean to say a reaction is reversible?

Answer 40

It means that it can go in both directions; reactants can turn into products, and products can turn back into reactants. This keeps happening until an equilibrium is reached, where both processes happen at the same rate and the amount of reactants and products stays the same.

Question 41

At equilibrium how does the rate of production of reactants compare to the rate of production of products? (compare the rates of the forward and reverse reactions)

Answer 41

The forward reaction drops and the reverse reaction raises.

Question 42

Does a reaction stop once it reaches equilibrium?

Answer 42

No, it still continues to happen.

Question 43

For the following reaction: 2CO(g) + O2(g) → 2CO2(g), if the system has reached equilibrium then more CO is added to the system, what happens to the concentration of CO2? Explain.

Answer 43

The concentration of Co2 becomes very concentrated.

Question 44

What is true about the concentration of reactants and products when a system reaches equilibrium?

Answer 44

The concentration of reactants decreases, while it increases for the products.

Question 45

What is gas pressure? What is happening at the particle level to produce the pressure?

Answer 45

Gas pressure is the force exerted by gas particles colliding with the wall of their container, at the particle level the pressure of a gas results from collisions between the gas particles and the walls of the container.

Question 46

What happens to the pressure of an enclosed gas when the temperature is increased? Why?

Answer 46

The pressure increases, which is because the molecules get more energy and then the pressure increases from the wall impacts.

Question 47

Explain the relationship between pressure and volume of a gas. If the volume of a gas goes down (shrink the container), what happens to the pressure?

Answer 47

The pressure increases as the volume decreases.