y 2 3 sec x 4

Chapter 6 Thermochemistry (Energy) Example: The hand warmers we all used during the winter are an example of thermochemistry. It involves the slow oxidation of iron. The amount of temperature rise depends on the size of your hand as well as what type of glove you’re wearing. Nature of Energy  Energy is the ability to do work  Work is a force acting over a distance  Heat is the flow of energy caused by a difference in temperature o Hand warmer and your hand  Energy can be exchanged between objects through contact o The hand warmer touching your hand Classification  Kinetic energy- energy in motion or energy being transferred o balls on a pool table rolling and hitting each other  Thermal energy- energy associated with heat o the energy associated with the hand warmers  Potential Energy- energy that is stored in an object, associated with composition and position o the pool balls at rest  Chemical Energy- energy associated with how the electrons are positioned in the nuclei Conservation of Energy  Law of conservation of Energy- energy cannot be created or destroyed o total energy at the beginning MUST equal total energy at the end System and Surrounding  System- the material or process within which we are studying the energy changes within o A pot of boiling water, the pot is the system  Surroundings- everything else with which the system can exchange energy o The air and everything else outside the pot of water  Conservation of energy means that the amount of energy gained or lost by the system equals the amount of energy gained by the surrounding Units  Kinetic energy is directly proportional to the mass and velocity o KE= ½ mv 2  mass is kg and velocity is m /s (kg* m /s )  Joule (J)- the amount of energy needed to move 1 kg of mass at a speed of 1 m/s  Calorie (cal)- the amount of energy needed to raise the temperature of 1g of water by 1 degree Celsius o 1 cal= 4.184 J o 1 Cal or (kilocalorie)= 4184 J st 1 Law of Thermochemistry  Law of Conservation of Energy  You cannot make a system that will produce energy without a source of energy o You must always have a source of energy ∆ = ∆ ℎ + ∆ ℎ Final amount = initial amount Δ (delta) is used to mean change Internal energy  the sum of the kinetic and potential energies of all the particles that make up the system  the change in the internal energy of a system only depends on the amount of energy in the system at the beginning and end o state function- mathematical function whose result only depends on the initial and final conditions not the process used ∆ = ∆ ℎ − ∆ ℎ ∆ ℎ = ∆ ℎ + ∆ ℎ Diagrams  “graphical” way of showing the direction of energy flow during a process  If reactants have a lower initial energy than products, the change in energy will be positive  If reactants have a higher initial energy, then the change in energy will be negative Flow in chemical reactions  In a reaction where carbon and oxygen come together there will be a net release of energy in the surroundings o C + O2 CO 2 o -ΔE reactionΔEsurroundings  In a reaction where carbon dioxide is coming apart then there will be an absorption of energy from surroundings to reactants o CO 2 C + O 2 o ΔE reaction-ΔEsurroundings Energy Flow (ΔE=qtw)  Energy is exchanged between the system and surroundings through heat and work o q= heat (thermal) energy o w= work energy o q and w are not state functions, they depend on the process Heat and Work  a soccer ball has 5J of kinetic energy  It loses .5 Joules of energy by friction from rolling across the grass  It hits another soccer ball and transfers it 4.5J of energy to the other soccer ball Heat exchange  Heat is the exchange of thermal energy between a system and surroundings  Occurs when the system and surrounding have different temperatures  Goes from high temperature to low temperature  Heat is absorbed-temperature goes up  Increase in temperature is directly proportional to the amount of heat absorbed  Proportionality constant is called heat capacity (c) o Units are Joule/ degrees Celsius or Joule/ Kelvin o q= c(ΔT) Heat Capacity of an Object  depends on amount of matter o usually measured by its mass  depends on type of material calculating  q=m*c *sΔT o m= (mass in g) o c =(joules/ grams * heat capacity) s o ΔT= (degrees Celsius)