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:𝐾𝐸 = 12∗ (𝑚𝑎𝑠𝑠) ∗ (𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦)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 ∗ (𝑚2𝑠2) 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) ∆𝐸 = 𝐸𝑓𝑖𝑛𝑎𝑙− 𝐸𝐼𝑛𝑖𝑡𝑖𝑎𝑙 this is the same as: ∆𝐸 = 𝐸𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠− 𝐸𝑅𝑒𝑎𝑐𝑡𝑎𝑛𝑡𝑠 - 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: −∆𝐸𝑆𝑦𝑠𝑡𝑒𝑚= ∆𝐸𝑠𝑢𝑟𝑟𝑜𝑢𝑛𝑑𝑖𝑛𝑔𝑠 - 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: ∆𝐸 = 𝑞 (ℎ𝑒𝑎𝑡)+ 𝑤(𝑤𝑜𝑟𝑘) - At constant volume change in internal energy is just equal to the heat at that volume. ∆𝐸𝑟𝑥𝑛= 𝑞𝑣 - 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. ∆𝐸𝑠𝑦𝑠𝑡𝑒𝑚= −∆𝐸𝑠𝑢𝑟𝑟𝑜𝑢𝑛𝑑𝑖𝑛𝑔𝑠 - Thermal Equilibrium when there is no additional net transfer of heat - Formula for Heat: 𝑞 (ℎ𝑒𝑎𝑡) = 𝐶 (ℎ𝑒𝑎𝑡 𝑐𝑎𝑝𝑎𝑐𝑖𝑡𝑦)∗ ∆𝑇(𝑡𝑒𝑚𝑝. 𝑐ℎ𝑎𝑛𝑔𝑒) - Formula for Heat w/ mass: 𝑞 = 𝑚(𝑚𝑎𝑠𝑠)∗ ∆𝑇 ∗ 𝐶𝑠 (𝑠𝑝𝑒𝑐𝑖𝑓𝑖𝑐 ℎ𝑒𝑎𝑡) *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= 𝑞 (ℎ𝑒𝑎𝑡)∆𝑇 (𝑡𝑒𝑚𝑝. 𝑐ℎ𝑎𝑛𝑔𝑒) = 𝐽 (𝑗𝑜𝑢𝑙𝑒𝑠)℃ (𝑡𝑒𝑚𝑝) - Specific Heat Capacity – 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 doesn’t 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* ΔV) Or vice versa. Pg.245 - To calculate the force or pressure: P= F/Area or F= P*Area - 1 L· 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: 𝑞𝑐𝑎𝑙 = 𝐶𝑐𝑎𝑙∗ ∆𝑇 - 𝐶𝑐𝑎𝑙 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.𝑞𝑐𝑎𝑙= −𝑞𝑟𝑥𝑛 - If everything is at constant volume: 𝑞𝑟𝑥𝑛= 𝑞𝑣= ∆𝐸𝑟𝑥𝑛 - Enthalpy (H) - the sum of internal energy and the product of pressure and volume 𝐻 = 𝐸 + 𝑃𝑉 - Formula for Change in Enthalpy: ∆𝐻 = ∆𝐸 + 𝑃∆𝑉 - Change in Enthalpy (ΔH) is the measure of heat exchanged under constant pressure. And only heat. - If heat is flowing out of the surroundings (exothermic) ΔH is negative. If heat is flowing into the system ΔH is positive (endothermic). - Rules for ΔH of a reaction: 1. If you multiply a chemical equation by a number you have to multiply ΔH by the same number A + B= C ΔH *1 2A +2B= 2C ΔH *2 2. If a chemical equation