semester 1 final

Energy Changes in Phase Transitions

Energy Change Calculation for Solid to Liquid Water

  • Initial state: 150 g of solid water at -10 °C

  • Final state: 150 g of liquid water at 0 °C

  • Temperature change: Heat from -10 °C to 0 °C

  • Energy change calculation:

    • Heat required to raise the temperature of solid water:

    • Specific heat of solid water: 0.50 cal/g°C

    • Energy required:
      E_1 = m imes c imes riangle T = 150 ext{g} imes 0.50 ext{cal/g°C} imes 10°C = 750 ext{cal}

    • Heat of fusion to convert ice to liquid water (at 0 °C):

    • Heat of fusion: 79.7 cal/g

    • Energy required for fusion:
      E_2 = m imes ext{heat of fusion} = 150 ext{g} imes 79.7 ext{cal/g} = 11955 ext{cal}

    • Total energy change (Etotal):
      E      { ext{total}} = E1 + E2 = 750 ext{cal} + 11955 ext{cal} = 12705 ext{cal}

Energy Change Calculation for Liquid Water Boiling

  • Initial state: 200 g of liquid water at 40 °C

  • Final state: 100 g of water boiled away at 100 °C

  • Temperature change: Heat from 40 °C to 100 °C

  • Energy change calculation:

    • Heat required to raise the temperature of liquid water:

    • Specific heat of liquid water: 1.0 cal/g°C

    • Energy required:
      E_1 = m imes c imes riangle T = 200 ext{g} imes 1.0 ext{cal/g°C} imes 60°C = 12000 ext{cal}

    • Heat of vaporization to convert liquid to gas at 100 °C:

    • Heat of vaporization: 540 cal/g

    • Energy required for vaporization:
      E_2 = m imes ext{heat of vaporization} = 100 ext{g} imes 540 ext{cal/g} = 54000 ext{cal}

    • Total energy change (Etotal):
      E      { ext{total}} = E1 + E2 = 12000 ext{cal} + 54000 ext{cal} = 66000 ext{cal}

Atomic Structure and Bonding

Determinants of Atomic Connectivity

  1. **Connections an atom can make in a bond depend on:

    • Valence electrons; the number of electrons in the outermost shell dictates bonding capability.

    • Groups and corresponding predictions:

      • Group 1: 1 connection

      • Group 2: 2 connections

      • Group 13: 3 connections

      • Group 14: 4 connections

      • Group 15: 3 connections

      • Group 16: 2 connections

      • Group 17: 1 connection

      • Group 18: 0 connections

Comparison of Ionic and Covalent Bonds

  1. Ionic vs. Covalent Bonds:

    • Ionic bonds:

      • Involves electron transfer from one atom to another, resulting in charged ions.

      • Generally occurs between metals and nonmetals.

    • Covalent bonds:

      • Involves sharing of electrons between atoms.

      • Typically occurs between nonmetals.

Definition and Concept of Polarity

  1. Polarity:

    • Defined as the distribution of electrical charge over the atoms joined by the bond.

    • Polar bonds: Result from differences in electronegativity between two bonded atoms, leading to partial positive and negative charges.

Molecular Polarity and Intermolecular Forces

  1. Molecular Polarity Effects:

    • Polar molecules have stronger intermolecular forces compared to nonpolar molecules due to their dipole moments.

Properties Indicating Attractive Forces

  1. Indicators of Attractive Forces:

    • Properties like evaporation rate, solubility, melting point, and boiling point serve as indicators of molecular attractive forces. A high boiling point typically indicates strong molecular attractions.

Identifying Elements, Compounds, and Mixtures

Characteristics

  1. Identification of substances:

    • Element: Consists of one type of atom, cannot be simplified further.

    • Compound: Consists of two or more different elements that are chemically bonded. Separation requires chemical methods.

    • Mixture: Physical combination of two or more substances; separation can be done via physical methods, and components retain individual properties.

Dimensional Analysis

Mathematical Computation Example

  1. Dimensional analysis for speed calculation:

    • Given: 45 miles

    • Conversion factor: 1 mile = 1609.34 meters

    • Time conversion: 1 hour = 3600 seconds

    • Computed speed:
      rac{45 ext{ miles}}{1} imes rac{1609.34 ext{ meters}}{1 ext{ mile}} imes rac{1 ext{ hour}}{3600 ext{ seconds}} = rac{45 imes 1609.34}{3600} ext{ m/s}, which equals approximately 33.528 m/s.

Periodic Properties

Reactivity Across the Periodic Table

  1. Reactivity Trends:

    • Reactivity generally decreases across a period for metals and increases for nonmetals because of increasing effective nuclear charge, attracting electrons more strongly.

Changes in Atomic Radius

  1. Atomic Radius Trends:

    • Increases from top to bottom in a group due to an increase in principal energy levels, leading to larger atomic sizes.

Density Trends in Elements

  1. Density Trends:

    • Generally increases from top to bottom in a group because atomic mass increases faster than atomic volume.

Energy Storage and Transfer in Changes

Energy Bar Graphs and Particle Representation

  1. Drawing energy bar graphs:

    • Indicate energy storage for thermal energy (Eth) and phase energy (Eph) during phase changes, including particle motion and spacing representation.