LA Chapter 7-9 Chemistry Study Guide PDF

Chapter 7 Thermochemistry Energy Energy: capacity to do work or transfer heat Thermochemistry: study of heat and energy in chemical reactions ○ “Thermo-” mean you are dealing with heat State function: describes the current state of a system. Independent of the path taken System and...

Chapter 7 Thermochemistry Energy Energy: capacity to do work or transfer heat Thermochemistry: study of heat and energy in chemical reactions ○ “Thermo-” mean you are dealing with heat State function: describes the current state of a system. Independent of the path taken System and surrounding: Work and energy System: specific part of a reaction where chemical changes are occuring Surrounding: everything outside of the system Universe: system and surroundings make up the universe Work: w When work is done ON the system, work has a POSITIVE value ○ Ex: a person is pushing a car in order for it to move The person (surrounding) is doing work on the car (system) When work is done BY the system, work has a NEGATIVE value ○ Ex: A moving car hits a person The car (system) is doing work on the person (surrounding) Law of conservation of energy: energy cannot be created or destroyed just transferred  - Energy can be transferred by heat or work ΔE = q + w Heat out (-) Work out (-) Heat in (+) Work in (+) + w: work done ON system + q: system has gained heat (from surroundings) - w: work done BY system - q: system has lost heat (given to surroundings) Energy done by the system - Change in system’s energy: E E E - Change in system’s internal energy can also be expressed as: E - When delta E is positive: the system GAINS energy - ENDOthermic: Endo=inside: thermic=heat : system gaining heat inside - When delta E is negative: the system LOSES energy - EXOthermic: Exo=outside: thermic=heat : system losing heat outside Pressure, Volume, Work Pressure-volume work: results from a change in volume by an external pressure on the system ○ Eq: Increase in volume, Positive V, work is negative Decrease in volume, Negative V, work is positive Ideal Gas Law (Chp 7): only consider gases cause it’s a “gas law”: PV=nRT Now, we can replace with to get another equation for work: R is the ideal gas constant: 8.314 J/mol*K T is Temp in Kelvin 1st Law of Thermodynamics Total energy of universe is constant →energy can move around 0 = ΔEsystem + ΔEsurroundings -qsys= qsurr -wsys= wsurr -ΔEsystem = + ΔEsurroundings System and surrounding: Heat Heat: q When heat is transferred from the surrounding TO the system, positive q value ○ Ex: A person’s hand heating an ice cube Person is the surrounding. Ice cube is the system. ○ The person is transferring their heat onto the ice cube. When heat is transferred from the system TO the surrounding, negative q value ○ Ex: The cold temperature freezes water left out The temperature is the surrounding. Water is the system. ○ The heat from liquid water is being transferred out so that it can freeze. First law of thermodynamics: the energy in the universe is constant  Specific heat capacity q = mCsΔT When do you use? When you need to calculate how much heat energy is required to change the temperature of a specific mass of a substance by a given amount Calorimetry - What is calorimetry: process to measure thermal (heat/energy) exchange - When heat is transferred from one object to another, and no heat is transferred to or from the surrounding, the heat gained or lost by the system is 0. - Ex: Metal placed in water scenario Isolated System Open System - Constant volume - Constant pressure - Bomb calorimeter - Coffee cup calorimeter q = CcalΔT ΔH = qp Heat exchanged @ constant Heat of cal pressure Heat capacity Enthalpy of cal - Sum of all internal energy Constant Pressure: Coffee cup Calorimetry - The heat absorbed or released (1st law of thermo) by the solution is equal and opposite to the heat absorbed or released by the reaction/system Please note this negative sign does not mean that heat of the solution is always Heat capacity of negative, it’s just a reminder water: 4.184 to switch signs J/g*C - To calculate qp: The change in heat of the reaction (under constant pressure) is equal to the change in enthalpy of the reaction: Enthalpy: H Enthalpy: Systems internal energy + Pressure*Volume ○ Eq: Change in Enthalpy: Endothermic: Delta H is POSITIVE ○ Heat is GAINED by the system Exothermic: Delta H is NEGATIVE ○ Heat is LOST from the system Hess’s Law: 3 Rules to follow to calculate enthalpy of a reaction 1) When an equation is reversed, the sign of its enthalpy changes: Product Reactant 2) When the coefficients in an equation are multiplied or divided by a factor, the enthalpy is also multiplied or divided by that same factor: Multiplied the equation by 2 3) When two or more reactions must be added together, their enthalpy values must also be added together Standard enthalpy of formation: You can use to calculate the standard enthalpy change for any reaction  Chapter 8+9 Quantum Model & Periodic Trends Concepts to know about light Longest Wavelength, Low frequency Short Wavelength, High Frequency Absorption: Going to higher energy levels ○ example: n=1 to n=2,3,4,5 etc Emission: Going to lower energy levels ○ example: n=5 to n=3,2,1 etc Ground state: lowest energy state of the set of electrons in the atom ○ Energy level closest to the nucleus Excited state: atom absorbs light of a specific energy. Atom has more energy than it does in its lowest state Paramagnetic: unpaired electrons, magnetic Diamagnetic: paired electrons, non magnetic Bohr model of atom Rydberg Equation When to use: when you need to calculate the wavelength of light emitted or absorbed by a hydrogen atom when its electron transitions between different energy levels Value of l Subshell 0 s 1 p 2 d 3 f  Subshells are made of orbitals: ○ s has 1 orbital ○ p has 3 orbitals ○ d has 5 orbitals ○ f has 7 orbitals Each orbital can only hold a maximum of TWO electrons So knowing this how many electrons can each subshell hold? Subshells, orbitals, electrons Electrons have shells=energy levels: denoted as n These shells are made of subshells: s, p, d, f ○ Groups of orbitals ○ From lowest energy to highest energy s