Thermochemistry Part 1 – Energy Copyright © The McGraw-Hill Companies, Inc.  Permission required for reproduction or display.

Energy is the capacity to do work Thermal energy is the energy associated with the random motion of atoms and molecules Chemical energy is the energy stored within the bonds of chemical substances Nuclear energy is the energy stored within the collection of neutrons and protons in the atom Electrical energy is the energy associated with the flow of electrons Potential energy is the energy available by virtue of an object’s position 6.1

Energy Changes in Chemical Reactions Heat is the transfer of thermal energy between two bodies that are at different temperatures. Temperature is a measure of the thermal energy. Temperature = Thermal Energy 400C 900C greater thermal energy

Thermochemistry is the study of heat change in chemical reactions. The system is the specific part of the universe that is of interest in the study. SURROUNDINGS SYSTEM open closed isolated Exchange: mass & energy energy nothing

Energy of the System Concepts The total energy of the system consists of potential energy and kinetic energy. Potential Energy (PE) – stored in chemical bonds Kinetic Energy (KE) – happens because of particle movement when bonds are broken and particles move to another position. Heat results from the transformation and movement of energy throughout the system. Energy generated through movement is called enthalpy (∆H). Temperature is a measure of the average KE (energy resulting from particle movement)

If the KE (temperature) at the end of the reaction is greater than the KE at the beginning, the reaction is exothermic. If the KE (temperature) at the end of the reaction is less than the KE at the beginning, the reaction is endothermic.

Analogy

2H2 (g) + O2 (g) 2H2O (l) + energy Exothermic process is any process that gives off heat – transfers thermal energy from the system to the surroundings. 2H2 (g) + O2 (g) 2H2O (l) + energy H2O (g) H2O (l) + energy Endothermic process is any process in which heat has to be supplied to the system from the surroundings. energy + H2O (s) H2O (l) energy + 2HgO (s) 2Hg (l) + O2 (g)

Calorimetry & Heat Snickers Commercial How much energy is there in a cashew?

Heat Capacity Heat Capacity is a measure of an object’s ability to absorb energy per degree temperature rise. ( J/oC ) Specific Heat Capacity is a measure of a substance’s ability to absorb energy per gram and degree temperature rise. ( J/goC ) Heat capacity is an Intensive Property!

q = mCDT Heat (q) absorbed or released: The specific heat (C) of a substance is the amount of heat (q) required to raise the temperature of one gram of the substance by one degree Celsius. Heat (q) absorbed or released: q = mCDT q: is heat, Joules or kilojoules m: mass in grams C: specific heat capacity DT: change in temperature,°C

Calorimetry Thermometer Stirrer Lid Reaction chamber