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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:πΎπΈ = 12β (πππ π ) β (π£ππππππ‘π¦)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 -Basically you measure KE in Joules (same as formula above) = 1kg β (π2π 2) 1 Calorie/Kilocalorie (Cal or kcal) =1000 cal = 4184J 1 Kilowatt-hour (kWh) = 3.60* 10^6 J - Calorie (cal) - the amount of energy required to raise the temperature of 1 g of water by 1 Celsius. - 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) βπΈ = πΈπππππβ πΈπΌπππ‘πππ this is the same as: βπΈ = πΈπππππ’ππ‘π β πΈπ ππππ‘πππ‘π - 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: ββπΈππ¦π π‘ππ= βπΈπ π’ππππ’ππππππ - 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) youβre 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: βπΈ = π (βπππ‘)+ π€(π€πππ) - At constant volume change in internal energy is just equal to the heat at that volume. βπΈππ₯π= ππ£ - Important Notes about the change of Internal Energy: - 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. βπΈπ π¦π π‘ππ= ββπΈπ π’ππππ’ππππππ - Thermal Equilibrium when there is no additional net transfer of heat - Formula for Heat: π (βπππ‘) = πΆ (βπππ‘ πππππππ‘π¦)β βπ(π‘πππ. πβππππ) - Formula for Heat w/ mass: π = π(πππ π )β βπ β πΆπ (π πππππππ βπππ‘) *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= π (βπππ‘)βπ (π‘πππ. πβππππ) = π½ (πππ’πππ )β (π‘πππ) - Specific Heat Capacity β amount of temp. required to raise the temp. of 1 gram of water by 1 Celsius - Molar Heat Capacity- amount of temp required to raise the temperature of 1 mole of a substance by 1 Celsius. Ex. Water has a high heat capacity (the temp. of water doesnβt change that much) - COME BACK PG.243- Pressure Volume Work- when the force from work is caused by volume change against external pressure - Formulas for Work: W (work) = F (force) *D (distance) W= P (pressure)*A (area)* Distance In this formula w and v must be opposite signs, so it could be this: W= - (P* ΞV) Or vice versa. Pg.245 - To calculate the force or pressure: P= F/Area or F= P*Area - 1 LΒ· atm= 101.3 J - Calorimetry- where you measure the change in temp. of the surroundings by thermal energy and surroundings change - 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: ππππ = πΆπππβ βπ - πΆπππ 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.ππππ= βπππ₯π - If everything is at constant volume: πππ₯π= ππ£= βπΈππ₯π - Enthalpy (H) - the sum of internal energy and the product of pressure and volume π» = πΈ + ππ - Formula for Change in Enthalpy: βπ» = βπΈ + πβπ - Change in Enthalpy (ΞH) is the measure of heat exchanged under constant pressure. And only heat. - If heat is flowing out of the surroundings (exothermic) ΞH is negative. If heat is flowing into the system ΞH is positive (endothermic). - Rules for ΞH of a reaction: 1. If you multiply a chemical equation by a number you have to multiply ΞH by the same number A + B= C ΞH *1 2A +2B= 2C ΞH *2 2. If a chemical equation

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