Chemistry Chapter 9 Energy and Chemistry

Chapter Objectives

  • Economic Importance of Energy Conversion

    • Discusses the significance of converting between different forms of energy and the realities of energy loss during those conversions.

  • Work and Heat Definitions

    • Understand standard sign conventions used for work and heat in thermodynamics.

  • State Functions

    • Define state functions and their relevance in thermodynamics.

  • First Law of Thermodynamics

    • State the law in both verbal and mathematical forms:
      ΔE=q+w\Delta E = q + w
      where $\Delta E$ is the change in internal energy, $q$ is heat, and $w$ is work.

  • Calorimetric Data Usage

    • Utilize calorimetric data to compute values of $\Delta E$ and $\Delta H$ for chemical reactions.

  • Standard Enthalpy of Formation (ΔHf°)

    • Define $\Delta H_f^\circ$ and illustrate formation reactions.

  • Understanding Hess’s Law

    • Explain Hess’s law in your own terms and calculate $\Delta H°$ from tabulated data.

Energy Use and the World Economy

  • Energy Consumption as Economic Indicator

    • Direct correlation exists between a country's energy consumption and its GDP.

  • Energy Supply Breakdown (2011)

    • Total energy supply in the USA was 107.66 quadrillion Btu.
    • Breakdown:
    • Domestic Production: 83.88 quadrillion Btu
    • Imports: 25.42 quadrillion Btu
    • Key sources: coal, natural gas, crude oil, nuclear energy, renewable energy.

  • Energy Consumption in 2016

    • Major components of energy consumption:
    • Residential: 21%
    • Commercial: 19%
    • Industrial: 32%
    • Transportation: 29%
    • Conversion losses constitute nearly two-thirds of energy for electricity generation.

Forms of Energy

  • Potential vs. Kinetic Energy

    • Potential Energy: Related to an object's position.
    • Kinetic Energy: Related to an object's motion.

  • Internal Energy: Combination of kinetic and potential energies of atoms in a system.

    • Chemical Energy: Energy exchanged during chemical reactions.

  • Other Energy Forms: Radiant, mechanical, thermal, electrical, and nuclear energies.

  • Thermochemistry: Analyzes energetics in chemical processes.

Heat and Work

  • Heat: Energy transfer between objects due to temperature difference; flows from hot to cold.
  • Work: Energy transfer involving applying a force over a distance.
  • Pressure-Volume Work (PV-work): Common in chemistry, illustrated by the action of releasing an inflated balloon.

Energy Units

  • Joule (J): SI unit of energy - defined as 1 J=1 kg m2/s21\, J = 1\, kg\, m^2/s^2
  • Other Units:
    • Btu: 1 Btu=1055 J1 \text{ Btu} = 1055\, J
    • Calorie: 1 calorie=4.184 J1 \text{ calorie} = 4.184\, J

Energy Transformation and Conservation

  • Conservation Principle: Total energy in a system must remain constant during transformations.
    • Energy can only change forms as heat ($q$) or work ($w$).
  • Change in Energy ($\Delta$):
    • Indicates the difference in energy states, where negative values mean energy release, and positive values mean absorption.
  • First Law of Thermodynamics: States energy can be transformed but not created or destroyed.

Waste Energy and Efficiency

  • Waste Energy: Unconvertable heat contributing to thermal pollution; cannot be completely transformed to work.
  • Efficiency Calculation: Expressed as a percentage, critical for increasing energy consumption efficiency.

Calorimetry

  • Calorimetry: Measuring heat flow in chemical reactions using calorimeters.
  • Key Factors Influencing Heat Absorption:
    • Amount of material ($m$ or $n$), type of material ($c$ or $C_p$), and temperature change ($\Delta T$).

Enthalpy

  • Enthalpy Changes ($\Delta H$):

    • Heat flow under constant pressure conditions.
    • Processes can be exothermic (releasing heat, ΔH<0\Delta H < 0) or endothermic (absorbing heat, ΔH>0\Delta H > 0).

  • Phase Changes:

    • Require heat (enthalpy) during transformations without a temperature change.
    • Examples include heat of vaporization ($\Delta H{vap}$) and heat of condensation ($\Delta H{cond}$).

Hess’s Law

  • Law Explanation: Enthalpy change is independent of the pathway taken during a reaction.
  • State Function: Depends only on current state, not the history of the system.

Energy and Stoichiometry

  • Thermochemical Equations: Convert between moles of reactants/products and energy changes.
  • Calculation Sequence: Steps to find energy from given amounts during reactions.

Example Calculations

  • Various Problems: Examples include calculating enthalpy changes using given weights, temperature changes, and utilizing calorimetric data to find specific heat potentials.

Conclusion on Energy Efficiency**:

  • Assessing economic factors in fuel energy density and thermochemical values is crucial for strategic fuel use and energy production optimization.