Energy and Chemical Reactions E = mc 2

SI Temperature: Kelvin o C Jacques Charles, Lord William Thompson Kelvin

Table – Kelvin/Celcius Comparison Event oCoC K Water Boils Body Temperature Room Temperature Water Freezes Absolute Zero

SI Temperature, Thermodynamics and Absolute Zero The SI unit of temperature, Kelvin, is based on the Kelvin temperature scale. 0 K or zero Kelvin (note the lack of the use of “degrees”) is defined as absolute zero. 0 K = o C Absolute zero is a theoretical temperature at which there is NO energy and NO motion. Thus, at absolute zero electrons would stop going around atoms. Scientist have been able to get within a microkelvin (uK) of absolute zero. They have never reached 0 K due to the slightest energy leaking into the Kelvin Temperature lab.

Celcius-Kelvin conversion is simple: o C = K – Example: What is 122 K in o C? 122 K – = o C K = o C Example: What is 26 o C in Kelvin? 26 o C = K

Units of Energy calorie and kilocalorie (cal and kcal or Cal) A calorie is the energy needed to raise 1 gram of water 1 o C.

Units of Energy Joule A Joule is the energy needed to accelerate a 1 kg object at 1 m/s 2 over a 1 m distance. 1 J = 1 kg. m 2 /s 2 1 cal = J

KMT – Kinetic Molecular Theory Matter is made of small particles (atoms and molecules). The particles are in constant, random motion. The particles are much smaller than the spaces between them. The motion and collisions of the particles can explain temperature, pressure, volume and reaction rate. un-to-imagine/jiggling-atoms

KMT Explains States of Matter Solid – slower moving particles, strong attractions, definite volume and shape. Liquid – particles move faster then solids, moderate intermolecular attractions, definite volume, no definite shape. Gas – rapidly moving particles, almost no intermolecular attractions, no definite volume, no definite shape.

Solid, liquid, or gas? SolidLiquidGas

KMT Explains Temperature Temperature is the average kinetic energy of the particles in a substance. The more rapid the motion, the hotter. Heat is the total thermal energy of a sample.

Which has a greater temperature? Which has more heat energy?

Boiling Point and Melting Point Boiling Point – The temperature at which a substance changes from liquid to gas at 1 atm of pressure. Melting Point – The temperature at which a substances changes from solid to liquid at 1 atm pressure. Between 290 K and 391 K, what phase is acetic acid in? Liquid

Phase Changes and Energy Temperature DOES NOT change during a phase change. The energy is being used to break or form attractions between particles. MP BP freezing melting condensation Vaporization (boiling) sublimation deposition

Energy Changes Energy can and often does change forms. Types: heat, electrical, nuclear (electromagnetic radiation), sound, light, kinetic (motion), gravitational potential (stored), chemical, etc.

Enthalpy heat of reaction and change in enthalpy are used interchangeably for a reaction at constant P ∆H = H products - H reactants endo: + ∆Hexo: - ∆H Reactants Products 2H 2 + O 2  2 H 2 O

Effects of a Catalyst on Activation Energy The catalyst speeds up the reaction by lowering the activation energy. Which graph is Exothermic? A B Which is Endothermic? In which graph is ΔH negative? In which graph is ΔH positive?

Calorimetry science of measuring heat calorimeter- device used to experimentally find the heat associated with a chemical reaction substances respond differently when heated

Heat Capacity (C) how much heat it takes to raise a substance’s T by one °C or K the amount of energy depends on the amount of substance

Heat Capacity specific heat capacity –(s) heat capacity per gram –in J/°C*g or J/K*g molar heat capacity – heat capacity per mole –in J/°C*mol or J/K*mol

Constant-Pressure Calorimetry when 2 reactants are mixed and T increases, the chemical reaction must be releasing heat so is exothermic the released energy from the reaction increases the motion of molecules, which in turn increases the T

Constant-Pressure Calorimetry If we assume that the calorimeter did not leak energy or absorb any itself (that all the energy was used to increase the T), we can find the energy released by the reaction: E released by rxn = E absorbed by soln ∆H ~ q q = mC∆T

Example 1 When 1 mol of CH 4 is burned at constant P, 890 kJ of heat is released. Find ∆H for burning of 5.8 g of CH 4 at constant P.