Thermochemistry -- The Flow of Energy: Heat --

Water Constants Solid 7.9 Liquid Gas 8.5

Thermochemistry -- The Flow of Energy: Heat -- Thermochemistry: the study of heat as it is transferred within a system and between a system and its surroundings Chemical potential energy: energy stored within the structural units of chemical substances

Thermochemistry -- The Flow of Energy: Heat -- Chemical System Types System typeDescription  q (change in heat) Endothermic System absorbing heat from the surroundings  q > 0 (positive) Exothermic System releasing heat to the surroundings  q < 0 (negative)

Heat vs. Temperature Heat (thermal energy) Total energy of all particles in a sample Temperature measure of the average energy of particles in a sample K = o C and o C = K - 273

Thermochemistry -- The Flow of Energy: Heat -- Law of Conservation of Energy: In any chemical or physical process, energy is neither created nor destroyed

Thermochemistry -- The Flow of Energy: Heat -- Heat Units calorie Expressed as a c (lower case) Quantity of heat needed to raise the temperature of 1 g of pure water 1  C Calorie Expressed as a C (upper case) Dietary Calorie 1 Calorie = 1 kilocalorie = 1000 calories

Units Joule SI unit of heat and energy Raises the temperature of 1 g of pure water  C J = 1 cal Thermochemistry -- The Flow of Energy: Heat --

Thermochemistry -- Video: Misconceptions about heat-- GJ0WHXMyE

Thermochemistry -- The Flow of Energy: Heat -- Heat Capacity (q) Amount of heat needed to increase the temperature of an object exactly 1  C Changes depending on the mass and chemical composition Specific Heat (C p ) Quantity of heat needed to raise the temperature of 1g of substance 1 o C Each substance has its own heat capacity.

Heat Capacity vs. Specific Heat Heat Capacity (q) Amount of heat needed to increase the temperature of an object exactly 1  C Specific Heat (C p ) Quantity of heat needed to raise the temperature of 1g of substance 1 o C Different q Same C p

Thermochemistry -- The Flow of Energy: Heat -- Application Example of Specific heat vs. Heat capacity Specific Heat of Aluminum J/gm K Heat Capacity of Aluminum g of Aluminum would take 90.2 joules

Thermochemistry -- The Flow of Energy: Heat -- Specific Heat Capacity Heat (q) specific heat capacity (C p ) Mass (m) change in temperature (  T) q = mC  T

Thermochemistry -- The Flow of Energy: Heat -- Example: How many kilojoules of heat are absorbed when 1.00 L of water is heated from 18  C to 85  C? Solution: q = mC  T q = 1000g x 4.18 J x 67 o C g o C q = 2.8E5 J 1 KJ 1000 J = 280 KJ

Thermochemistry -- The Flow of Energy: Heat -- Example: A chunk of silver has a heat capacity of 42.8 J/  C. If the silver has a mass of 181 g, calculate the specific heat of silver. Solution: q = mC  T 42.8 J = 181g x C x 1 O C C = J/g o C

Thermochemistry -- Measuring and Expressing Heat Changes -- Your Turn: The temperature of a piece of copper with a mass of 95.4 g increases from 20.0 o C to 40.0 o C when the metal absorbs 849 J of heat. What is the specific heat of copper? q = mC  T 849 J = 95.4g x C x 20.0 o C C = 0.45 J/g x o C

Thermochemistry -- Measuring and Expressing Heat Changes -- Calorimetery: The science of measuring heat