4: Module 4
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We have already established that quantities are important in science, especially in chemistry. It is important to make accurate measurements of a variety of quantities when performing experiments. However, it is also important to be able to relate one measured quantity to another, unmeasured quantity. In this chapter, we will consider how we manipulate quantities to relate them to each other.
- 4.1: Stoichiometry
- Quantities of substances can be related to each other using balanced chemical equations.
- 4.2: The Mole
- The mole is a key unit in chemistry. The molar mass of a substance, in grams, is numerically equal to one atom's or molecule's mass in atomic mass units.
- 4.3: The Mole in Chemical Reactions
- Balanced chemical reactions are balanced in terms of moles. A balanced chemical reaction gives equivalences in moles that allow stoichiometry calculations to be performed.
- 4.4: Mole-Mass and Mass-Mass Calculations
- Mole quantities of one substance can be related to mass quantities using a balanced chemical equation. Mass quantities of one substance can be related to mass quantities using a balanced chemical equation. In all cases, quantities of a substance must be converted to moles before the balanced chemical equation can be used to convert to moles of another substance.
- 4.5: Yields
- Theoretical yield is the calculated yield using the balanced chemical reaction. Actual yield is what is actually obtained in a chemical reaction. Percent yield is a comparison of the actual yield with the theoretical yield.
- 4.6: Limiting Reagents
- The limiting reagent is the reactant that produces the least amount of product. Mass-mass calculations can determine how much product is produced, and how much of the other reactants remain.
- 4.7: Energy
- Energy is the ability to do work and uses the unit joule. The law of conservation of energy states that the total energy of an isolated system does not increase or decrease.
- 4.8: Work and Heat
- Work can be defined as a gas changing volume against a constant external pressure. Heat is the transfer of energy due to temperature differences. Heat can be calculated in terms of mass, temperature change, and specific heat.
- 4.9: Enthalpy and Chemical Reactions
- Every chemical reaction occurs with a concurrent change in energy. The change in enthalpy, a kind of energy, equals heat at constant pressure. Enthalpy changes can be expressed by using thermochemical equations. Enthalpy changes are measured by using calorimetry.
- 4.10: Intermolecular Forces
- All substances experience dispersion forces between their particles. Substances that are polar experience dipole-dipole interactions. Substances with covalent bonds between an H atom and N, O, or F atoms experience hydrogen bonding. The preferred phase of a substance depends on the strength of the intermolecular force and the energy of the particles.
- 4.11: Phase Transitions - Melting, Boiling, and Subliming
- Phase changes can occur between any two phases of matter. All phase changes occur with a simultaneous change in energy. All phase changes are isothermal.
- 4.12: Prelude to Solutions
- A solution is a homogeneous mixture-a mixture of two or more substances that are so intimately mixed that the mixture behaves in many ways like a single substance. Many chemical reactions occur when the reactants are dissolved in solution. In this chapter, we will introduce concepts that are applicable to solutions and the chemical reactions that occur in them.
- 4.13: Definitions
- Solutions are composed of a solvent (major component) and a solute (minor component). Concentration is the expression of the amount of solute in a given amount of solvent and can be described by several qualitative terms. Solubility is a specific amount of solute that can dissolve in a given amount of solvent. "Like dissolves like" is a useful rule for deciding if a solute will be soluble in a solvent.
- 4.14: Quantitative Units of Concentration
- Quantitative units of concentration include molarity, molality, mass percentage, parts per thousand, parts per million, and parts per billion.
- 4.15: Dilutions and Concentrations
- Calculate the new concentration or volume for a dilution or concentration of a solution.
- 4.16: Concentrations as Conversion Factors
- Concentration units can be used as conversion factors.