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Book Notes for Chemistry 2 Test 1 Chapter 6 Thermochemistry An means multiplication For ex 1 4 4 Thermochemistry is the relationship between Chemistry and Energy Energy is the capacity to do work and work is force acting through a distance Mnemonic It takes energy to go to work and work means you always have to force yourself to drive a distance Heat is a flow of energy caused by different temperature Kinetic energy is energy associated with object motion Thermal energy deals with the movement of molecules and is a type of kinetic energy The more you move the more thermal energy you have Potential energy is associated with object position and composition Chemical energy is also associated with positions of electrons molecules and nuclei This makes Chemical energy a form of potential energy Law of Conservation of Energy Energy cannot be created nor destroyed Remainder is loss as heat in the surroundings 1st Law of Thermodynamics also law of energy conservation says energy in the Universe is constant because no energy can be created nor destroyed Kinetic Energy Formula 2 1 2 Remember In the kinetic energy formula mass must be in kilograms kg and velocity must be in m s Units of Energy 1 calorie cal 4 184 joules J 1 Joule 1kg 2 2 Basically you measure KE in Joules same as formula above 1 Calorie Kilocalorie Cal or kcal 1000 cal 4184J 1 Kilowatt hour kWh 3 60 10 6 J 1 Celsius Calorie cal the amount of energy required to raise the temperature of 1 g of water by Internal energy E is the sum of kinetic and potential energies Internal energy depends on only the current state of the system not how it got to that state Means it is a state function Which means that the difference is always between its final and initial values Internal Energy Change this is the same as So the products minus the reactants Reactants have higher internal Energy causing exothermic reactions to be negative If Reactants have higher internal energy than Products then energy change in the system is negative and energy change of the surroundings is positive If vice versa The products have higher internal energy then the surroundings is negative and the system is positive Think about it like this If you have too much energy in the beginning reactants you re going to lose some of that energy to your surroundings causing reactants to be negative But if you do not have enough energy in the beginning then you will gain some energy in your system reactants from your surroundings products Think of everything balancing Energy cannot be created nor destroyed The formula for Change in Internal Energy Important Notes about the change of Internal Energy At constant volume change in internal energy is just equal to the heat at that volume Heat and work are not state functions do not depend on current state Also means q can be greater than w and vice versa The change in internal energy the sum of q and w is always constant Energy leaving carries a negative sign Energy lost equals the amount of energy gained by the surroundings Ex Thermal Equilibrium when there is no additional net transfer of heat Formula for Heat Formula for Heat w mass Delta T is in Celsius and specific heat capacity is in J g Celsius Heat capacity C the measure of a systems ability to absorb thermal energy w o a large temperature change Formula for Heat Capacity C by 1 Celsius substance by 1 Celsius COME BACK PG 243 Specific Heat Capacity amount of temp required to raise the temp of 1 gram of water Molar Heat Capacity amount of temp required to raise the temperature of 1 mole of a Ex Water has a high heat capacity the temp of water doesn t change that much Pressure Volume Work when the force from work is caused by volume change against In this formula w and v must be opposite signs so it could be this external pressure Formulas for Work W work F force D distance W P pressure A area Distance W P V Or vice versa Pg 245 To calculate the force or pressure P F Area or F P Area 1 L atm 101 3 J energy and surroundings change Calorimetry where you measure the change in temp of the surroundings by thermal Bomb Calorimeter measures internal energy for combustion reactions keeps it at a constant volume Internal energy equals heat at constant volume Formula for Heat when using a Bomb Calorimeter is heat capacity of the entire calorimeter If no heat escapes from the calorimeter the amount of heat gained is the exact amount released However they still need opposite signs for ex If everything is at constant volume Enthalpy H the sum of internal energy and the product of pressure and volume Formula for Change in Enthalpy And only heat Change in Enthalpy H is the measure of heat exchanged under constant pressure If heat is flowing out of the surroundings exothermic H is negative If heat is flowing into the system H is positive endothermic Rules for H of a reaction number 1 If you multiply a chemical equation by a number you have to multiply H by the same 2 If a chemical equation reversed then H changes its sign A B C H 1 2A 2B 2C H 2 A B C H C A B H 3 If the chemical equation is expressed in as the sum of a series of steps then is equal to sum of all the heats from each step Hess s Law 2 1 2 2 2 2 3 1 2 For the 3rd Rule Hess s law the goal is to cross them out after you get them all balanced So if you have diff rows you can multiply or divide them by different numbers to get them to cross out Remember you can also flip reactions which turn them from Standard States and Standard Enthalpy Formations Help us determine the change in Enthalpy Difference in Enthalpy by products and reactants by helping assign a zero negative to positive value 1 Standard States Gas Pure gas at the pressure of 1 atm Liquid or Solid Pure substance at its most stable form at 1 atm and usually at 25 degrees Celsius Substance in a solution Concentration of 1 M 2 Standard Enthalpy Change H says the change in enthalpy occurs when all products have a degree sign which indicates their standard states 3 Standard Enthalpy of Formation or Standard Heat of Formation Pure Compound When 1 mol of the compound forms from its constituent elements in their standard states Its standard state is when 0 Pure Element For Most Compounds Standard Enthalpy Heat of Formation is negative More Rules about Standard Enthalpy Heat of Formation Elements Compound Compound Elements reactants Fossil fuels are finite do not last forever Chapter 13 Chemical Kinetics change in time decrease Reaction rate the negative of the change in

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USF CHM 2046 - Test 1

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