Chemical Reactions: Key Concepts & Reaction Stoichiometry

Greenhouse gases like carbon dioxide, methane, and water vapor allow sunlight to pass through the atmosphere and warm the Earth's surface. They also absorb and re-emit infrared radiation, trapping heat within the atmosphere. This process is crucial for maintaining Earth's temperature.
The balance between incoming solar radiation and outgoing infrared radiation determines Earth's average temperature. An increase in greenhouse gases can disrupt this balance, leading to a rise in global temperatures.

The average atmospheric temperature has risen by approximately 0.7°C (1.3°F) since 1860, with more pronounced warming in recent decades.
Atmospheric CO_2 levels have increased by 38% during the same period, primarily due to human activities such as burning fossil fuels and deforestation.
Combustion of fossil fuels (coal, oil, and natural gas) and volcanic action release CO2 into the atmosphere, contributing to the greenhouse effect and global warming. Additionally, deforestation reduces the planet's capacity to absorb CO2.

A chemical reaction involves the conversion of one or more substances (reactants) into different substances (products) through the breaking and forming of chemical bonds.
A combustion reaction is a specific type of chemical reaction in which a substance combines rapidly with oxygen, typically producing heat and light. It often results in the formation of oxygen-containing compounds.

Chemical equations are a shorthand way of describing a chemical reaction, providing information on:
- Chemical formulas of reactants and products involved in the reaction.
- Physical states of reactants and products (e.g., gas, liquid, solid, aqueous).
- Relative numbers of reactant and product molecules or moles, indicated by coefficients.

Chemical equations must be balanced to obey the Law of Conservation of Mass, which states that matter cannot be created or destroyed in a chemical reaction.
Balancing involves adjusting coefficients in front of chemical formulas to ensure that the number of atoms of each element is the same on both sides of the equation.

Balanced chemical equations provide quantitative relationships between the amounts of reactants and products involved in a chemical reaction. These relationships are expressed in terms of moles.
Stoichiometry is the study of the numerical relationships between chemical quantities (e.g., moles, mass, volume) in a chemical reaction. It allows for the prediction of reactant and product amounts.

Ratios derived from balanced chemical equations serve as conversion factors between moles of reactants and products.
Example: 2 C8H{18} + 25 O2 \rightarrow 16 CO2 + 18 H2O. The ratio of 2 moles of C8H{18} to 16 moles of CO2 can be used to calculate the amount of CO2 produced from a given amount of C8H_{18}.

Molar mass is a conversion factor that relates the mass of a substance to its number of moles. It is expressed in grams per mole (g/mol).
Coefficients from balanced equations convert between moles of reactants and products.

The limiting reactant is the reactant that is completely consumed first in a chemical reaction. It determines the maximum amount of product that can be formed.
Theoretical yield is the maximum amount of product that can be produced based on the amount of the limiting reactant, assuming perfect reaction conditions.
Actual yield is the actual amount of product obtained from a chemical reaction, which is often less than the theoretical yield due to factors such as incomplete reactions or side reactions.
Percent yield is calculated as: \frac{\text{actual yield}}{\text{theoretical yield}} \times 100\%. It indicates the efficiency of a chemical reaction.

To determine the limiting reactant, calculate the amount of product that each reactant could produce based on the stoichiometry of the balanced equation. The reactant that produces the smaller amount of product is the limiting reactant.

Combustion reactions involve the rapid reaction of a substance with O_2, producing oxygen-containing compounds and heat.
Example: CH4(g) + 2 O2(g) \rightarrow CO2(g) + 2 H2O(g)

Alkali metals (Group 1 elements) react vigorously with nonmetals, such as sodium reacting with chlorine to form sodium chloride (table salt).
Alkali metals also react with water to form dissolved alkali metal ions, hydroxide ions, and hydrogen gas: 2M(s) + 2H2O(l) \rightarrow 2M^+(aq) + 2OH^-(aq) + H2(g)

Halogens (Group 17 elements) react with metals to form metal halides, such as sodium reacting with chlorine to form sodium chloride.
Halogens react with hydrogen to form hydrogen halides: H2 + X2 \rightarrow 2HX
Halogens react with each other to form interhalogen compounds, such as bromine reacting with fluorine: Br2 + F2 \rightarrow 2BrF