ch 7

Question 1

1. what is avogadro’s #

2. In a chemical formula, what do the subscripts tell us (concerning moles)?

Answer 1

1. 6.02 x 10^23 it is the number of pieces in a mole
2. The subscripts tell us how many moles of each element there are in a mole. Ie: CO2 1 mole of Carbon and 2 moles of Oxygen

Question 2

1. What is the molar mass of an element?

2. To what place do we round molar mass?

Answer 2

1. It is the weight of one mole of the element in grams. It is the atomic mass in grams. Ex: The atomic mass of Na is 22.99amu. It is also 22.99g. One mole of Na weighs 22.99g.
2. either the tenths place, or use 3 significant figures.

Question 3

1. How are chemical equations written?
2. What does the delta sign above the arrow indicate?
3. a chemical reaction must always be …………. Why?
4. How do we balance an equation?
5. Can we change the subscripts when balancing equations?

Answer 3

1. reactants on L and products on right, with an arrow separating them. Multiple reactants or products are separated by a + sign
2. The delta sign above the arrow indicates that heat is used to start the reaction
3. Balanced. Because atoms are neither created nor destroyed in a reaction, but merely shuffled around. Therefore, the numbers must be equal on either side of an equation.
4. We use coefficients before each element starting with the most complex formula. Make sure coefficients are to the lowest ration ie: instead of 2 and 4, you would use 1 and 2
5. No. Changing subscripts actually changes the molecules rather than changing the number of molecules.

Question 4

1-5 what are the 5 types of reactions, and briefly explain each.

6. What is spontaneous combustion?

Answer 4

1. combination: 2 or more reactants combine to form 1 product. 2Mg+O2 = 2MgO
2. Decomposition: one substance splits into
   two or more simpler substances.
   2HgO = 2Hg + O2
3. single replacement: one element takes the
   place of a different element.
   Zn + 2Hcl = ZnCl2 + H2
4. Double replacement: the positive ions in the reactant compounds switch places.
   AgNO3 + NaCl = AgCl + NaNO3
5. combustion reaction: a carbon-containing compound burns in oxygen gas to form carbon dioxide (CO2) and water (H2O)
   energy is released as a product in the form of heat
   CH4 + 2O2 = CO2 + 2H2O + energy

6.Occurs due to high internal energy due to oxidation in presence of moisture or bacterial content

Question 5

1. What are oxidation/reduction reactions?
2. When electrons are lost, the element is ………….. . When electrons are gained, the element is …………….. .

Answer 5

1. electrons are transferred from one substance to another.

2. Oxidized (OIL). Reduced (RIG)

Question 6

The law of conservation of mass indicates that in an ordinary chemical reaction 1, 2, 3

Answer 6

1. matter cannot be created or destroyed
2. no change in total mass occurs
3. the mass of products is equal to the mass of reactants

Question 7

1. What are the 3 criteria that must be met for a reaction to occur?
2. If heat is in the product side of a reaction what type of reaction is it? If heat is in the reactant side of the equaction what type of reaction is it?
3. If the heat of products is less than reactants, what type of reaction is it?

Answer 7

1. Collision, Orientation, and Energy
2. Exothermic, endothermic
3. Endothermic.