TOPIC: ENERGY Do Now:

All physical & chemical changes are accompanied by change in energy The chemistry of energy changes is known as Thermochemistry!

Stability and Energy If energy is high, stability is low If energy is low, stability is high

Energy: Ability to do Work The SI unit for an energy measurement is called the Joule (J) EXAMPLE: 1 Joule = amount of energy required to lift a golf ball 1 meter

Other Energy Units: calorie, Calorie, BTU’s 1 calorie = 4.18 Joules 1 Calorie = 1000 calories = 1 kilocalorie NOTE: When your body breaks down food, these reactions give off heat – which is measured in calories (That’s why your food is labelled in calories)

Law of Conservation of Energy Energy is neither created nor destroyed in ordinary chemical or physical change, rather it can be converted from one form to another Energy before = Energy after - potential to kinetic- radiant to electric - electric to heat- chemical to kinetic - chemical to electrical

(Not a complete list!) Energy Mechanical – large enough to see KineticPotential Non-mechanical – too small to see ChemicalHeatLightElectricalNuclear

Kinetic Energy (KE) – energy of motion KE = ½ x Mass x Velocity 2 = ½ mV 2 KE depends on how heavy and how fast Kinetic Molecular Theory: the atoms and molecules making up substances are in constant motion

Potential Energy (PE): energy of position; stored energy of matter EXAMPLES  stapler  Rubberband

When Potential energy is released from matter it becomes kinetic energy

Energy in Chemistry = chemical energy heat energy

Chemical Energy energy stored in bonds Bonds are stable You need energy to break bonds Energy is released when bonds are formed

EXOTHERMIC If the overall energy in a chemical reaction is negative (meaning energy is released) = the rxn is exothermic energy (heat) is given off = exothermic EXO - energy leaves system (exits)

Environment System Energy Exothermic Rxn Temperature of environment  Temperature of system 

ENDOTHERMIC If the overall energy in a chemical reaction is positive (meaning energy is absorbed) = the rxn is endothermic energy (heat) is absorbed = endothermic Endo - Energy enters system (enter)

Environment System Energy Temperature of environment  Temperature of system  ENDOTHERMIC

Energy of Universe is conserved Universe Environment System Energy Energy can move between the system and the environment

Calorimeter: an insulated devise used for measuring the amount of heat absorbed or released during a chemical or physical change

“universe” is contained in Styrofoam cup “environment” is water**** “system” is whatever put in water Energy lost = Energy gained Difficult to monitor “system” Easy to monitor “environment” (water) Energy lost/gained by environment = Energy gained/lost by system

Calorimetry 10 grams of NaOH is dissolved in 100 g of water & the temperature of the water increases from 22  C to 30  C was dissolving process endothermic or exothermic how do you know? Exothermic – temperature of environment ↑

Heat Energy  Heat: energy that is in the process of flowing from warmer object to a cooler object  Symbol for heat energy = Q or q  The amount of heat required to raise the temp. of 1 gram of water 1 0 C = a calorie

The amount of heat transferred depends on 3 things Temperature change Mass of substance Specific Heat of substance

Specific Heat The amount of heat required to raise the temp of any given substance by 1 0 C Symbol = c Specific heat = a physical constant unique for each pure substance Found in Table B

Calculating Heat Transferred Q = mC  T Simple system: pure substance in single phase calculate heat gained or lost using: Q = amount of heat transferred m = mass of substance C = specific heat capacity of the substance.  T = temperature change = T final – T initial

Calorimetry problem from before 10 grams of NaOH is dissolved in 100 g of water & the temperature of the water increases from 22  C to 30  C We already said it’s exothermic – now we can actually calculate the amount of heat energy released Energy lost by NaOH (system) = Energy gained by water (environment) Environment Energy

What’s happening when NaOH dissolves? Add H 2 O NaOH close together, not interacting Na + and OH - ions pulled apart & interacting with H 2 O

Q = mC  T Q = energy (joules) M = mass (grams) C = specific heat capacity (Table B)  T = temperature change = T f - T i Q = ? M = M = Well, temp change was for water, so want mass of water m = 100 g C = specific heat capacity (Table B) = 4.18 J/gK  T =  T = temperature of water increased from 22  C to 30  C  30  C -22  C = 8  C =  T

Q = mC  T Q = (100 g)(4.18 J/g  C  (8  C) Q = 3344 Joules