Temperature Conversions and Heating Curves

Temperature Scales and Conversions

Temperature is a fundamental physical property measured in different units. The most common temperature scales in chemistry are Celsius (°C), Kelvin (K), and Fahrenheit (°F).

• Celsius (°C): Based on the freezing (0°C) and boiling (100°C) points of water.

• Kelvin (K): The SI unit for temperature. Absolute zero (0 K) is the lowest possible temperature.

• Fahrenheit (°F): Commonly used in the United States.

Key Conversion Formulas:

Heating Curves: A heating curve shows how the temperature of a substance changes as heat is added, illustrating phase changes (solid, liquid, gas).

• Plateaus on the curve represent phase changes (melting, boiling).

• Sloped regions represent temperature changes within a single phase.

Calculations Involving Significant Figures and Rounding

Significant Figures (Sig Figs)

Significant figures reflect the precision of a measured or calculated quantity.

• Rules:

  • All nonzero digits are significant.

  • Zeros between nonzero digits are significant.

  • Leading zeros are not significant.

  • Trailing zeros are significant only if there is a decimal point.

• Rounding: Round the final answer to the correct number of significant figures based on the operation:

  • Multiplication/Division: Use the least number of sig figs from the input values.

  • Addition/Subtraction: Use the least number of decimal places from the input values.

Conversion Factors, Units, and Derived Units

Conversion Factors

Conversion factors are ratios used to express a quantity in different units without changing its value.

• Example:

• To convert, multiply by the appropriate conversion factor.

Units and Derived Units

• Base Units: Fundamental units (meter, kilogram, second, etc.).

• Derived Units: Combinations of base units (e.g., m/s, g/cm3).

Density, Mass, Temperature, Volume, and Length

Definitions and Relationships

• Density (d): The mass per unit volume of a substance.

  • Formula:

  • Units: g/mL, g/cm3, kg/L

• Mass (m): The amount of matter in an object (grams, kilograms).

• Volume (V): The amount of space an object occupies (mL, L, cm3).

• Length: Distance measurement (meters, centimeters, millimeters).

Density Calculations

Solving for Mass, Volume, or Density

• Given any two of mass, volume, or density, the third can be calculated using .

• Example: If a sample has a mass of 25.0 g and a volume of 5.00 mL, its density is .

Homogeneous vs. Heterogeneous Mixtures

Types of Mixtures

• Homogeneous Mixture: Uniform composition throughout (e.g., salt water, air).

• Heterogeneous Mixture: Non-uniform composition; different parts are visible (e.g., salad, sand in water).

Metric Unit Equivalents

Common Metric Prefixes and Equivalents

• Examples: 1 kg = 1000 g; 1 mL = 0.001 L

Periodic Table Categories and Trends

Categories of Elements

• Metals: Good conductors, malleable, ductile, shiny.

• Nonmetals: Poor conductors, brittle, dull.

• Metalloids: Properties intermediate between metals and nonmetals.

Periodic Table Trends

• Atomic Radius: Increases down a group, decreases across a period.

• Ionization Energy: Decreases down a group, increases across a period.

• Electronegativity: Decreases down a group, increases across a period.

Potential vs. Kinetic Energy

Forms of Energy

• Potential Energy: Stored energy due to position or composition (e.g., chemical bonds, a rock at the top of a hill).

• Kinetic Energy: Energy of motion (e.g., moving particles, flowing water).

Calculations Involving Specific Heat

Specific Heat and Heat Calculations

• Specific Heat (c): The amount of heat required to raise the temperature of 1 gram of a substance by 1°C.

• Formula:

• Where:

  • q = heat (Joules, J)

  • m = mass (grams, g)

  • c = specific heat (J/g·°C)

  • ΔT = change in temperature (°C)

• Example: How much heat is needed to raise 10.0 g of water by 5.0°C? (c for water = 4.18 J/g·°C)

Changes of State

Physical Changes Between States of Matter

• Melting: Solid to liquid

• Freezing: Liquid to solid

• Vaporization (Boiling): Liquid to gas

• Condensation: Gas to liquid

• Sublimation: Solid to gas

• Deposition: Gas to solid

Periodic Table, Atom, and Subatomic Particles

Structure of the Atom

• Subatomic Particles:

  • Proton: Positive charge, mass ≈ 1 amu, located in nucleus

  • Neutron: No charge, mass ≈ 1 amu, located in nucleus

  • Electron: Negative charge, mass ≈ 0.0005 amu, located outside nucleus

• Atomic Number (Z): Number of protons in the nucleus; defines the element.

• Mass Number (A): Total number of protons and neutrons in the nucleus.

• Isotopes: Atoms of the same element with different numbers of neutrons.

States of Matter

Solid, Liquid, Gas

• Solid: Definite shape and volume; particles are closely packed and vibrate in place.

• Liquid: Definite volume, indefinite shape; particles are close but can move past each other.

• Gas: Indefinite shape and volume; particles are far apart and move freely.

Electron Arrangements

Electron Configuration

• Electrons are arranged in energy levels (shells) around the nucleus.

• Each shell can hold a specific number of electrons: 2 in the first, 8 in the second, 18 in the third, etc.

• Example: Carbon (atomic number 6): 2 electrons in the first shell, 4 in the second (2,4).

Summary Table: Subatomic Particles