Chemical Reactions, Equations, and Metric Conversions in GOB Chemistry

Equations for Chemical Reactions

Chemical Change

A chemical change occurs when a substance is converted into one or more new substances with different formulas and properties. Chemical changes are fundamental to chemistry and are observed in everyday life, such as the rusting of iron or the tarnishing of silver.

• Indicators of chemical change: Formation of bubbles, color change, production of a solid (precipitate), or heat that is produced or absorbed.

• Example: Iron (Fe) reacts with oxygen (O2) to form rust (Fe2O3).

Writing Chemical Equations

Structure of a Chemical Equation

A chemical equation represents the reactants and products in a chemical reaction. It uses formulas and symbols to describe the transformation.

• Reactants are written on the left side of the arrow (→); products are on the right.

• Multiple reactants or products are separated by a + sign.

• The delta (Δ) symbol above the arrow indicates heat is used to start the reaction.

• Physical states are indicated in parentheses: (s) for solid, (l) for liquid, (g) for gas, (aq) for aqueous (dissolved in water).

General format:

• reactant + reactant Δ product + product

Symbols Used in Chemical Equations

The following table summarizes common symbols used in chemical equations:

Symbol	Meaning
+	Separates two or more formulas
→	Reacts to form products
Δ →	Reactants are heated
(s)	Solid
(l)	Liquid
(g)	Gas
(aq)	Aqueous

Balancing Chemical Equations

Principle of Balancing

A balanced chemical equation has equal numbers of each type of atom on both sides of the equation. This reflects the law of conservation of mass: atoms are neither created nor destroyed in a chemical reaction.

• Example: $\mathrm{C(s) + O_2(g) \xrightarrow{\Delta} CO_2(g)}$

• Reactant atoms: C = 1, O = 2; Product atoms: C = 1, O = 2

Steps for Balancing Chemical Equations

1. Write the equation using correct formulas for reactants and products.

2. Count the atoms of each element in the reactants and products.

3. Use coefficients to balance each element, starting with the most complex formula.

4. Check the final equation to confirm it is balanced and coefficients are in the lowest ratio.

Example:

• Unbalanced: $\mathrm{Al(s) + S(s) \rightarrow Al_2S_3(s)}$

• Balanced: $\mathrm{2Al(s) + 3S(s) \rightarrow Al_2S_3(s)}$

Balancing Equations with Polyatomic Ions

Polyatomic ions can often be balanced as units if they appear unchanged on both sides of the equation.

• Example: $\mathrm{Na_3PO_4(aq) + MgCl_2(aq) \rightarrow Mg_3(PO_4)_2(s) + NaCl(aq)}$

• Balance the phosphate ion (PO43-) as a unit.

Types of Chemical Reactions

Classification of Reactions

Chemical reactions are classified into several types based on the changes that occur:

• Combination (Synthesis) Reaction: Two or more substances combine to form one product. Example: $\mathrm{2Na(s) + Cl_2(g) \rightarrow 2NaCl(s)}$

• Decomposition Reaction: One substance splits into two or more simpler substances. Example: $\mathrm{2HgO(s) \rightarrow 2Hg(l) + O_2(g)}$

• Single Replacement Reaction: One element replaces another in a compound. Example: $\mathrm{Fe(s) + CuSO_4(aq) \rightarrow FeSO_4(aq) + Cu(s)}$

• Double Replacement Reaction: Positive ions in two compounds switch places. Example: $\mathrm{AgNO_3(aq) + NaCl(aq) \rightarrow AgCl(s) + NaNO_3(aq)}$

• Combustion Reaction: A carbon-containing compound burns in oxygen to form CO2 and H2O, releasing energy. Example: $\mathrm{CH_4(g) + 2O_2(g) \rightarrow CO_2(g) + 2H_2O(g) + \text{energy}}$

Summary Table: Types of Chemical Reactions

Type	General Equation	Example
Combination	A + B → AB	$\mathrm{2Na(s) + Cl_2(g) \rightarrow 2NaCl(s)}$
Decomposition	AB → A + B	$\mathrm{2HgO(s) \rightarrow 2Hg(l) + O_2(g)}$
Single Replacement	A + BC → AC + B	$\mathrm{Fe(s) + CuSO_4(aq) \rightarrow FeSO_4(aq) + Cu(s)}$
Double Replacement	AB + CD → AD + CB	$\mathrm{AgNO_3(aq) + NaCl(aq) \rightarrow AgCl(s) + NaNO_3(aq)}$
Combustion	Hydrocarbon + O2 → CO2 + H2O + energy	$\mathrm{CH_4(g) + 2O_2(g) \rightarrow CO_2(g) + 2H_2O(g)}$

Oxidation-Reduction (Redox) Reactions

Definition and Importance

Oxidation-reduction (redox) reactions involve the transfer of electrons between substances. These reactions are essential for energy production in biological systems and for processes such as corrosion and combustion.

• Oxidation: Loss of electrons, addition of oxygen, or loss of hydrogen.

• Reduction: Gain of electrons, loss of oxygen, or gain of hydrogen.

• Mnemonic: "OIL RIG" – Oxidation Is Loss, Reduction Is Gain (of electrons).

• Example: $\mathrm{4Fe(s) + 3O_2(g) \rightarrow 2Fe_2O_3(s)}$ (iron rusting)

Characteristics of Oxidation and Reduction

Process	Involves	May Involve
Oxidation	Loss of electrons	Addition of oxygen, loss of hydrogen
Reduction	Gain of electrons	Loss of oxygen, gain of hydrogen

Redox in Biological Systems

Biochemical molecules such as FAD (flavin adenine dinucleotide) undergo redox reactions, transferring hydrogen atoms and electrons to produce energy.

• Example: $\mathrm{CH_3OH \rightarrow H_2CO + 2H}$ (oxidation: loss of H atoms)

• Intermediate products in metabolism can be toxic if not properly processed.

Metric and SI Prefixes

Metric System Prefixes

The metric system uses prefixes to indicate multiples or fractions of units. These prefixes are essential for expressing measurements in science and health fields.

• Kilo- (k): $10^3$ times the unit (e.g., 1 km = 1000 m)

• Milli- (m): $10^{-3}$ times the unit (e.g., 1 mg = 0.001 g)

• Micro- (μ): $10^{-6}$ times the unit (e.g., 1 μg = 0.000001 g)

Common Metric Equalities

• $1\,\mathrm{kg} = 1000\,\mathrm{g}$

• $1\,\mathrm{g} = 1000\,\mathrm{mg}$

• $1\,\mathrm{mg} = 1000\,\mathrm{\mu g}$

• $1\,\mathrm{L} = 1000\,\mathrm{mL}$

• $1\,\mathrm{cm}^3 = 1\,\mathrm{mL}$

Conversion Factors

Conversion factors are ratios derived from equalities and are used to convert between units.

• Example: $1\,\mathrm{kg} = 2.20\,\mathrm{lb}$

• Conversion factors: $\frac{1\,\mathrm{kg}}{2.20\,\mathrm{lb}}$ and $\frac{2.20\,\mathrm{lb}}{1\,\mathrm{kg}}$

Steps for Unit Conversion

1. State the given and needed quantities.

2. Write a plan to convert the given unit to the needed unit.

3. State the equalities and conversion factors.

4. Set up the problem to cancel units and calculate the answer.

Example: Convert 164 lb to kg. $164\,\mathrm{lb} \times \frac{1\,\mathrm{kg}}{2.20\,\mathrm{lb}} = 74.5\,\mathrm{kg}$

Toxicology and LD50

LD50 Values

The LD50 (lethal dose, 50%) is a measure of toxicity, representing the dose required to kill half the members of a tested population. It is usually expressed in mg/kg of body mass.

• Example: The LD50 of caffeine is 192 mg/kg.

• Lower LD50 values indicate higher toxicity.

Applications in Health Sciences

• Metric units are used to express nutrient requirements, drug dosages, and toxicity levels.

• Risk assessment involves exposing laboratory animals to substances and monitoring health effects.

Additional info: Some content was inferred and expanded for completeness, including the explanation of redox reactions in biological systems and the use of conversion factors in health sciences.