UNIT 4: Quantifying Reactions

Question 1

what should the total mass before and after a reaction be?

Answer 1

the total mass before and after the reaction should be the same

Question 2

what is one mole equal to?

Answer 2

6.022x10^23

Question 3

what’s a hydrate

Answer 3

an ionic compound that has absorbed water. A certain number of water molecules can co-crystallize with the salt.

Ex:Na2SO4 ∙ 10H2O (sodium sulfate decahydrate)
MgCl2 ∙ 6H2O (magnesium chloride hexahydrate)

Question 4

what does anhydrous mean

Answer 4

without water

Question 5

whats the steps to calculating a hydrate

Answer 5

First, calculate the number of moles of anhydrous salt. Next calculate the number of moles of water. Last, calculate the ratio of the two in order to determine the formula of the hydrate

Question 6

what does structural formulas tell you

Answer 6

exact # of atoms in a molecule

Question 7

what does a chemical formulas tell you about a molecule

Answer 7

is a compact representation of a chemical. For covalent compounds, this is also called the compound’s molecular formula.

Question 8

what does empirical formulas tell you about a molecule

Answer 8

reduces the subscripts in the molecular formula to the smallest whole numbers.

Question 9

how do you convert mass percentages to formulas

Answer 9

1) Assume you have 100 g

2) Convert the masses of each element
to moles

3) Divide each number of moles by the
smallest number of moles to get the ratios

Question 10

whats the law of conservation of mass

Answer 10

Matter cannot be created or destroyed.

In a chemical reaction, the EXACT number and type of atoms NEVER changes. This is why we balance reactions.

Question 11

whats a combustion reaction

Answer 11

A combustion reaction is any reaction involving a fuel and an oxidant and usually accompanied by a flame.

Combustion reactions are exothermic
(they give off heat).

Combustion reactions require energy to
get started (activation energy).

Question 12

what are the products of combustion dependent on, in order to make water?

Answer 12

The products of combustion reactions depend on the reactants. If the fuel contains hydrogen, water must be a product of combustion. Also, the water will ALWAYS be in the form of steam.

Question 13

what makes the products of carbon dioxide in a combustion reaction

Answer 13

If the fuel contains carbon, carbon dioxide will be a product of combustion if there is enough oxygen. If there is enough oxygen, the reaction is called “complete combustion.”

Question 14

whats an incomplete combustion

Answer 14

If there is NOT enough oxygen, a mixture of carbon dioxide, carbon monoxide, and carbon soot will be produced.

Carbon monoxide is extremely toxic and is the #1 cause of poisoning deaths in the U.S.

Carbon monoxide is also flammable.

Question 15

whats a combustion reaction

Answer 15

A combination reaction is any reaction in which ONE product is made from the combination of two (or more) reactants. The reactants are often pure elements. Combination reactions are also called synthesis reactions.

Question 16

whats a decomposition reaction

Answer 16

A decomposition reaction is any reaction in which one reactant decomposes, or breaks down, into two or more products. A decomposition reaction is the reverse of a combination reaction.

Question 17

whats an acid base reaction

Answer 17

In an acid base reaction, there is a transfer of one or more hydrogen ion(s) from the acid to the base. The hydrogen ion is H+. Often water is a product. Sometimes a gas, like CO2 is given off.

Question 18

single replacement reaction

Answer 18

In a single replacement reaction (aka single displacement reaction), there are two reactants and two products. One of the reactants is in its elemental form, and one of the products is in its elemental form. In the single replacement reaction, one element (or polyatomic ion) trades partners.

Question 19

whats a double replacement reaction

Answer 19

This reaction is called a double replacement
reaction because both reactants are changing
partners. The insoluble CaCO3 is a precipitate

Question 20

what do all double replacement reactions have

Answer 20

1) 2 reactants and 2 products (all ionic compounds)
2) Both reactants switch partners
3) At least one product is insoluble, indicated by (s)

Question 21

whats a theoretical yield

Answer 21

The amount of product you should get if the reaction works perfectly.

Question 22

when would you not get a theoretical yield

Answer 22

The reaction does not work “perfectly”
Some reactant does not react
Some product gets blown away
Some product gets stuck to the container
Equipment errors
Human errors
Etc.

Question 23

actual yield

Answer 23

what you measure in the lab. It is how much you actually got in real life.

Question 24

percent yield of reaction

Answer 24

The Percent Yield of a reaction is a measure of how well it worked.

Question 25

how do you calculate the percent yield

Answer 25

actual yield/ theoretical yield x 100%

Question 26

whats a limiting reagent

Answer 26

1. The Limiting Reagent of a reaction is the reactant that limits the amount of product formed.