Balancing Chemical Equations
Chemical equations must be balanced because matter cannot be created or destroyed. All of the atoms that we begin with in a chemical reaction we must also end with. What is the name of this law?
Law of Conservation of Mass
Identify the following reaction as synthesis, decomposition, single displacement, or double displacement
2H2O2 --> 2H2O + O2
Decompostion
AB --> A + B
Find the molar mass of O2
16 x 2 = 32 g
How many grams are in 3.4 moles of H2O?
3.4 moles x (18 grams/1 mole) = 61.2 grams
In his gold foil experiment, Rutherford shot alpha particles at a sheet of gold foil only a couple atoms thick. Most of the alpha particles (positively charged) went right through the foil while a couple bounced back. What did Rutherford conclude about the structure of the atom from this experiment?
Atoms are mostly empty space with a positively charged nucleus
12 grams of sugar are mixed into 100 grams of water. The mixture is stirred until the water dissolves. What is the total mass of the mixture?
12 g sugar + 100 g water = 112 g mixture
Identify the following reaction as synthesis, decomposition, single displacement, or double displacement
Zn + CuCl2 --> ZnCl2 + Cu
Single displacement
- ionic compounds
- a metal and a metal switch places OR a nonmetal and a nonmetal switches places
- on both sides of the equation a single element is alone
Find the molar mass of CaCO3
Ca = 40
C = 12
O = 16 x 3 = 48
Total = 100 g
What is the theoretical yield of water if 10 grams of oxygen are used?
C3H8 + 5O2 --> 4H2O + 3CO2
10 g O2 x (1 mole/32 g O2) x (4 moles H2O/5 moles O2) x (18 g H2O) = 4.5 grams H2O
Al+3 and O-2 bond to form aluminum oxide. What is the correct formula for aluminum oxide?
Al2O3
BaCl2 + (NH4)2CO3 --> BaCO3 + 2NH4Cl
How many nitrogen, hydrogen and carbon atoms are on the reactants side of the equation? Your answer should be in the following format:
N =
H =
C =
N = 2
H = 8
C = 1
Identify the following reaction as synthesis, decomposition, single displacement, or double displacement
KNO3 + AlCl3 --> Al(NO3)3 + KCl
Double displacement
-- two ionic compounds
-- the metals switch places OR the nonmetals switch places
Find the molar mass of Ca(NO3)2
Ca = 40
N = 14 x 2
O = 16 X 6
Total = 164 g
CaCl2 + 2Na --> Ca + 2NaCl
100 molecules of CaCl2 and 100 molecules of Na are used in the reaction above. What is the theoretical yield of NaCl?
100 molecules CaCl2 x (2 molecule NaCl/1 molecule CaCl2) = 200 molecules NaCl
100 molecules Na x (2 molecule NaCl/2 molecule CaCl2) = 100 molecules NaCl
Theoretical yield = 100 molecules NaCl
Na+1 and P-3 bond to form sodium phosphide. What is the correct formula for sodium phosphide?
Na3P
Given the following reaction. Write the correct coefficients so it is balanced.
____C3H8 +___ O2 --> ___H2O + ___CO2
C3H8 + 5O2 --> 4H2O + 3CO2
C = 3 C = 3
H = 8 H = 8
O = 10 O = 10
Based on the equation below. What are the typical reactants and products of a combustion reaction?
CxHy + O2 --> H2O + CO2
Typical reactants: hydrocarbons and oxygen gas
Typical products: water and carbon dioxide
What is the percent composition by mass of CO2
Total mass = 44g
Carbon = 12/44 = 27%
Oxygen = 32/44 = 73%
Carbon 27%, Oxygen 73%
2H2O + O2 --> 2H2O2
10 molecules of H2O and 10 molecules of O2 are used to produce H2O2 through the chemical reaction above. What is the limiting reactant?
10 molecules H2O x (2 molecules H2O2/2 molecules H2O) = 10 molecules H2O2
10 molecules O2 x (2 molecules H2O2/1 molecules O2) = 20 molecules H2O2
H2O is the limiting reactant
Na and Cl bond to form table salt. What is the best explanation (in terms of valence electron activity) for why these two elements bond?
Sodium has one valence electron in its outer shell while chlorine has seven. Atoms want to get to 8 to become stable so sodium will donate an electron to chlorine to fill its octet
Given the following reaction. Write the correct coefficients so it is balanced.
_____CH4 + _____Cl2 --> _____CCl4 + _____HCl
CH4 + 4Cl2 --> CCl4 + 4HCl
Use the chemicals below to write a combustion reaction. Hint: You DO NOT need to use all of the chemicals
C5H7 O2 H2 CO2 C H2O
C5H7 + O2 --> H2O + CO2
Follows the format: CxHy + O2 --> H2O + CO2
What is the percent composition by mass of H2O?
Total mass = 18 g
H = 2/18 = 11%
O = 16/18 = 89%
Oxygen 89%, Hydrogen 11%
According to a student's calculations 100 grams of water should decomposed to produce 11 grams of hydrogen gas. However, there was a leak in the container and only 9 grams of hydrogen were produced. What is the percent yield of this reaction?
(9 / 11) x 100 = 82%
(actual / theoretical) X 100 = percent yield
Which of the following is an example of chemical change?
Folding paper
Burning paper to form carbon dioxide and water
Dissolving paper in water
Cutting paper
Burning paper to form carbon dioxide and water
New chemicals are formed that have unique chemical structures and properties (different from the reactants)