Measurements and Energy KEY QUESTIONS THE BIG PICTURE How can I use dimensional analysis to make chemistry problems easier How can chemical thermodynamics help me to understand energy Remember Energy is stored in molecules How can we use it What are the standard units of measure in chemistry What forces drive chemical reactions and how can a chemist harness them By the end of Today s Lecture you should know SI units and metric conversions Accuracy and precision Internal energy and the First Law of Thermodynamics State Functions CH110 FA10 SAS Ballot for use in class 1 Exam 1 Concepts You Should Know Chapter 2 Nomenclature What do the numbers on the periodic table mean How do we name common ions acids etc Chapter 3 Chemical Formulas What is mass percent What is a mole What is molecular weight What are the empirical formula and the molecular formula of a compound Chapter 6 Energy Atoms Orbitals and the Origins of the Periodic Table What is the relationship between photons their wavelength their frequency and their energy How does all that stuff about photons help chemists to understand the nature of atoms What is an orbital How is it defined What is the electron configuration of an atom How do I represent it How do the shape size and number of orbitals help me to understand the periodic table CH110 FA10 SAS 2 Exam 1 Concepts You Should Know Chapter 7 Periodic Trends What are ionization energy electron affinity and electronegativity What are the trends in atomic size How are the sizes of atoms and ions related How do these show up in the periodic table Chapter 8 Bonding and Lewis Structures What are the three types of bonding How do we describe bonding in ionic solids How is covalent bonding described in terms of enthalpy strength bond order etc What is a Lewis structure What do we learn about a molecule when we see that it has more than one Lewis structure How do you use the octet rule and its violations to help predict Lewis structures CH110 FA10 SAS 3 Scientific Measurement 1 Metric Measurement SI Units mass length time temperature energy 2 Important prefixes you must know mega M kilo k centi c milli m micro nano n CH110 FA10 SAS 4 Scientific Measurement 3 Significant Figures How many significant figures are there in each of these numbers Which has the most Is it even unambiguous 854 0 00854 85400 4 Uncertainties How sure am I that two numbers are actually different If my calculator reports a decimal to eight digits should I use them all in my answer CH110 FA10 SAS 5 Unit Conversions Dimensional analysis and careful unit conversion are critical to success Ex 1 A laser emits 488 nm light What is this wavelength in meters In centimeters CH110 FA10 SAS 6 Unit Conversions Exam Format An unknown liquid has a density of 2 14 g mL How many mL would a 6 42 g sample of this liquid occupy A B C D E 3 00x10 3 mL 2 14 mL 3 00 mL 6 42 mL 2 14x103 mL CH110 FA10 SAS 7 Uncertainties in Scientific Measurement Precision Accuracy Measurements are not perfect Scientists learn about the world around us through How certain can we be that a given measurement yields the correct answer CH110 FA10 SAS 8 Energy and Thermodynamics Thermodynamics Thermochemistry mechanical kinetic energy 1 2mv2 potential energy mass in a place where force can act electrical moving charge Q1Q2 d electrostatic light photons chemical sound bonds molecules moving uniformly nuclear heat binding energy molecules moving randomly gravitational mgh where g 9 8 m s2 CH110 FA10 SAS 9 Units of Energy SI unit Joule J KE of a 2 kg object moving at 1 m per second using 1 2 mv2 or PE of 100 g at height 1 m using mgh In chemistry kilojoule 1 kJ calorie 1 cal Calorie dietary 1 Cal CH110 FA10 SAS 10 First Law of Thermodynamics Law of conservation of energy Energy can be from one form to another but the total energy all energy lost by a under observation must be gained by the and vice versa during energy conversion some heat is always produced CH110 FA10 SAS 11 Exothermic and Endothermic Exothermic energy System Surroundings E Endothermic energy Surroundings System CH110 FA10 SAS E 12 State Functions State Function A elevation B elevation a state function its value depend on past history Distance traveled a state function Time to bottom a state function CH110 FA10 SAS 13 Internal Energy E Internal Energy E E Efinal Einitial Quantitative definition The capacity to or E E is a state function CH110 FA10 SAS 14 Another Useful State Function Enthalpy H H qp Defined as Energy transferred when P is constant think of our lake example with dams blocking the streams Chemical reactions are commonly run at constant pressure atmospheric pressure we will frequently refer to energy and enthalpy interchangeably CH110 FA10 SAS 15 What You Should Know Units and Basic Dimensional Algebra How do I manipulate exponents How do I perform metric conversions What are significant figures Energy and State Functions What is the First Law of Thermodynamics What is meant by system and surroundings What is the difference between an endothermic or exothermic process What is a State Function What is the meaning of Internal Energy and what is it composed of What is the meaning of Enthalpy CH110 FA10 SAS 16