22 terms

Equations and balancing chemical reactions

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Chemical change
Occurs when a substance is converted into one or more new substances that have different formulas and different properties.

Example, when silver tarnishes, the shiny silver metal (Ag), reacts with sulfur, S to become the dull, black substance we call tarnish (Ag2S)
Chemical reactions
always involves chemical change because atoms of the reacting substances form new combinations with new properties,

Example, a chemical reaction takes place when a piece of iron (Fe) combines with oxygen (O2) in the air to produce a new substance, rust (Fe2O3)
Evidence of chemical reaction
1. change in color
2. formation of a gas( bubbles)-not boiling
3. formation of a solid (precipitate)
4. heat (or a flame) produces or heat absorbed.
chemical equation
-tells us the materials we need and the products that will form
-the formulas of the reactants are written on the left of the arrow and the formulas of the products on the right.
Symbols used in writing equations
+ seperates two or more formulas
→ reacts to form products
Δ⟶ reactants are heated
(s) solid
(l) liquid
(g) gas
(aq) aqueous - substance is dissolved in water
what happens to the bonds between the atoms during chemical reaction
When a chemical reaction takes place, the bonds between the atoms of the reactants are broken and new bonds are formed to give the products.
all atoms are conserved which means that atoms cannot be gained, lost, or changed into other types of atoms during a chemical reaction.
Balanced equation
every chemical reactions must be written as a balanced equation, which shows the same number of atoms for each element in the reactants as well as in the products.
coeffiicients
in the balanced equation, there are whole numbers called coefficients in front of the formulas.
Law of Conservation of matter
matter cannot be created or destroyed during a chemical reaction.
indicate the number of each type of the atom in the balanced equation
Fe2S3(s) + 6HCL (aq) → 2FeCl3 (aq) + 3H2S(g)
reactants/products
Fe 2 (1x2) 2(2x1)
S 3 (1x3) 3 (3x1)
H 6 (6x1) 6 (3x2)
Cl 6(6x1) 6(2x3)
the chemical reaction of methane, CH4, and oxygen gas, O2, produces carbon dioxide (CO2) and water (H2O). write the balanced equation.
CH4 (g) + O2(g) Δ⟶ CO2(g) + H2O (g)

CH4 (g) + 2O2(g) Δ⟶ CO2(g) + 2H2O (g)
Al(s) + Cl2 (g) ⟶ AlCl3(s)
2Al(s) + 3Cl2 (g) ⟶ 2AlCl3(s)
Balancing chemical equations with Poly atomic ions
Na3PO4 (aq) + MgCl2 (aq) ⟶ Mg3(PO4)2 (s) +NaCl (aq)
2Na3PO4(aq) + 3MgCl2 (aq) ⟶Mg3(PO4)2 (s) + 6NaCl (aq)
Balance
Pb(NO3)2 (aq) +AlBr3(aq) ⟶ PbBr2 (s) + Al(NO3)3 (aq)
3Pb(NO3)2 (aq) +2AlBr3(aq) ⟶ 3PbBr2 (s) + 2Al(NO3)3 (aq)
N2 (g) + O2 (g) ⟶ NO (g)
N2 (g) + O2 (g) ⟶ 2NO (g)
lithium metal reacts with liquid water to form hydrogen gas and aqueous lithium hydroxide
Li (s) + H2O (l) ⟶ H2 (g) + LiOH (aq)

2Li (s) + 2H2O (l) ⟶ H2 (g) + 2 LiOH (aq)
solid phosphorous reacts with chlorine gas to form solid phosphorus pentachloride
P (s) + Cl2 (g) ⟶ PCl5 (s)

2P (s) + 5Cl2 (g) ⟶ 2PCl5 (s)
solid iron (II) oxide reacts with carbon monoxide gas to form solid iron and carbon dioxide gas
FeO (s) + CO (g) ⟶ Fe (s) + CO2 (g)

balanced because O+O=O2 on the reactants =
O2 on the product side
liquid pentene (C5H10) burns in oxygen gas to form carbon dioxide gas and water vapor.
C5H10 +O2 ⟶ CO2 +H20

2C5H10 + 15O2 ⟶ 10CO2 + 10H20
hydrogen sulfide gas and solid iron (III) chloride react to form solid iron (III) sulfide and hydrogen chloride gas
H2S (g) + FeCl3 (s) ⟶ Fe2S3(s) + HCl (g)

3H2S (g) +2 FeCl3 (s) ⟶ Fe2S3(s) + 6HCl (g)
Clinical Application

In the body, the amino acid alanine C3H7NO2 (aq) reacts with O2 gas to produce gaseous carbon dioxide, liquid water, and urea, CH4N2O (aq). write the balanced equation.
C3H7NO2 + O2 ⟶ CO2 + H2O +CH4N2O

2C3H7NO2 + 6O2 ⟶ 5CO2 + 5H2O +CH4N2O
balance
Mg (s) + AgNO3 (aq) ⟶ Mg (NO3)2 (aq) + Ag (s)
Mg (s) + AgNO3 (aq) ⟶ Mg(NO3)2 (aq) + Ag (s)

Mg (s) + 2AgNO3 (aq) ⟶ Mg (NO3)2 (aq) + 2Ag (s)