THERMOCHEMISTRY AND THERMODYNAMICS Ch. 16: Energy and Chemical Change

Questions to ponder What does thermodynamic mean? (hint: break up the word) 2. How do we measure energy? 3. What is temperature measuring? -thermo= to do w/ temp. or heat -dynamic= energetic motion or change - Calories the kinetic energy of the surrounding molecules

Energy (E) The ability to do work or produce heat ; the sum of all potential and kinetic energy in a system is known as the internal energy of the system

Potential energy In chemistry potential energy is the energy stored in a substance because of its composition - generally stored in chemical bonds

Kinetic energy Energy of motion, usually of particles, proportional to Kelvin temperature

Law of Conservation of Energy 1st Law of Thermodynamics: - Energy cannot be created nor destroyed energy of the universe is constant

Heat (q) Transfer of energy in a process (flows from a warmer object to a cooler one – heat transfers because of temperature difference but, remember, temperature is not a measure of energy—it just reflects the motion of particles)

Measuring Heat calorie- amount of heat required to heat one gram of water one degree Celsius *note: this is different to a Calorie we eat Joule (J)- is the SI unit to measure energy Conversion factor: 4.184 J = 1 cal

Calorimeter - insulated device used to measure the amount of heat absorbed by the system.

Specific Heat (c) The amount of energy required to raise the temperature of one gram of ANY substance, one degree Celsius.

Specific heat of water (liquid state) = 4.184 J/gC ( or 1.00 cal/g C) Water has one of the highest specific heats known! That is why the earth stays at such an even temperature all year round! Cool huh? Heat lost by substance = heat gained by water (if this does not happen, calculate the heat capacity of the substance)

System - Area of the universe we are focusing on (i. e System - Area of the universe we are focusing on (i.e., the experiment) Surroundings - everything outside of the system System + Surroundings = universe

Endothermic - net absorption of energy (heat) by the system; energy is a reactant; (i.e., baking soda and vinegar when mixed get very cold to the touch)

A Classic ENDOthermic reaction! The equation for the reaction is: Ba(OH)2  8 H2O(s ) + 2 NH4SCN(s ) --> Ba(SCN)2(s ) + 10 H2O(l ) + 2 NH3(g )

Exothermic – net release of energy (heat) by the system; energy is a product;

Calculating Heat ∆T = T(final) - T(initial) q = (c)(m)(∆T) Heat=(specific heat)(mass)(change in Temp.) ∆T = T(final) - T(initial)

Thermochemistry The study of heat changes that accompany chemical reactions and phase changes.