Slide 1 / 118 Slide 2 / 118 Thermochemistry Slide 3 / 118 Slide 4 / 118 Table of Contents · The Nature of Energy The Nature of Energy · State Functions** Click on the topic to go to that section · Enthalpy Measuring Enthalpy Changes: Calorimetry · Energy Associated with Changes of State · Return to Enthalpies of Reaction · Table of Hess's Law Contents · · Enthalpies of Formation · Energy in Foods and Fuels Slide 5 / 118 Slide 6 / 118 Pr A Review of Energy from Physics es Thermochemistry en at Potential Energy is the energy that objects have energy due to their position. Gravitational Potential Energy GPE = mgh Elastic Potential Energy EPE = 1/2 kx 2 We know chemical and physical processes release and absorb energy. We use these thermochemical principles to design air Electric Potential Energy conditioners and refrigerators as well as foot warmers that allow us to stay comfortable as we "go big" on the hill! U E = kQ 1 Q 2 r 2
Slide 7 / 118 Slide 8 / 118 A Review of Energy from Physics A Review of Energy from Physics An outside force can change The total energy of Kinetic Energy is the energy that an object has by the energy of a system by an isolated system is virtue of its motion: doing work on it. constant. KE = 1/2 mv 2 work Algebraically, these two statements combine to become: Work is defined by the formula E 0 + W = E f W = Fd parallel Since E f - E o = ∆ E, this can also be written as ∆ E = W Slide 9 / 118 Slide 10 / 118 1 A reaction produces 3.8 cal of energy. How many joules Units of Energy of energy is produced? The SI unit of energy is the Joule (J). Another unit of energy is the calorie (cal). 1 cal = 4.184 J The energy of food is measured in Calories (C). [note the capital "C"] 1 Calorie = 1000 calories = 4184 Joules Slide 11 / 118 Slide 12 / 118 2 A reaction uses 235 J of energy. How many calories 3 A 20 ounce coke contains 240 Calories. How many kilojoules of energy are present in a 20 ounce Coke? have been burned?
Slide 13 / 118 Slide 14 / 118 The First Law of Thermodynamics Energy & Heat ∆E = w + q From last year, we know that ∆ E = W. Energy is neither created nor destroyed. This year, we extend that by adding another way to change the energy of a system; by the flow of Heat (q). In other words, the total energy of the universe is a constant; if the system loses energy, it must be gained by the surroundings, When two objects of different temperature are in contact, heat flow and vice versa. results in an increase of the energy of the cooler object and an identical decrease of the energy of the hotter object. Initial Final Internal energy, E E 0 Internal energy, E state E state Energy A B T = 10 ℃ lost to T = 20 ℃ E < E 0 E > E 0 surroundings ∆ E < 0 ( - ) ∆ E > 0 ( + ) Energy gained heat flow Final Initial from state state surroundings ∆E = w + q E E 0 E of system decreases E of system increases *Note, we use a lower case "w" in chemistry. Slide 15 / 118 Slide 16 / 118 System and Surroundings Changes in Internal Energy When considering energy changes, we need to focus on a well- defined, limited part of the universe. The portion we focus on is called the system and everything else is called the If ∆ E > 0, E final > E initial surroundings. H 2 (g) + O 2 (g) The system absorbed energy Consider the following reaction occurring within a metal cylinder. from the surroundings. 2H 2 (g) + O 2 (g) --> 2H 2 O(g) Internal energy, E ∆ E < 0 ∆ E >0 (negative) (positive) Surroundings If ∆ E < 0, E final < E initial The system includes the reactants and products (here, the hydrogen, oxygen The system released energy and water molecules). from the surroundings. H 2 O(l) system The surroundings are everything else (here, the cylinder and piston). Slide 17 / 118 Slide 18 / 118 4 Ten grams of table salt in dissolved in water in a 250 mL 5 When a strong acid is added to a flask containing water beaker. Which of the following is a component of the the flask becomes warm to the touch. This is because... system? A the reaction performed work on the flask A NaCl B the system absorbed heat from the surroundings E A and B B water C the system released heat to the surroundings F A, B, and C C Na+ D the surroundings released heat to the system G A, B, and D D beaker
Slide 19 / 118 Slide 20 / 118 6 When a strong acid is added to a flask containing water Changes in Internal Energy the flask becomes warm to the touch. Which correctly describes the change in energy? A ∆ E sys is positive and ∆ E sur is negative System When energy is exchanged between the system and the B ∆ E sys is positive and ∆E sur is positive Heat q > 0 surroundings, it is either exchanged as either heat ( q ) C ∆ E sys is negative and ∆ E sur is positive or work ( w ). Surroundings D ∆ E sys is negative and ∆ E sur is negative ∆ E = q + w Work w > 0 ∆ E>0 Slide 21 / 118 Slide 22 / 118 7 The ∆E of a system that gains 50 kJ of heat and q , w , ∆ E, and Their Signs performs 24 kJ of work on the surroundings is ________ kJ. A -74 Sign Conventions for q, w and ∆ E B -26 q + system gains heat - system loses heat C 0 D +26 + w work done on system - work done by system E +74 ∆ E + net gain of energy by system - net loss of energy by system Slide 23 / 118 Slide 24 / 118 9 The ∆ E of a system that absorbs 120 J of heat and 8 The ∆ E of a system that releases 120 J of heat does 120 J of work on the surroundings is and does 40 J of work on the surroundings is ________ J. ________ J. A -240 A -80 B -120 B -160 C 0 0 C D +120 +80 D E +240 +160 E
Slide 25 / 118 Slide 26 / 118 10 The ∆ E of a system that absorbs 12,000 J of heat Exchange of Heat between and the surrounding does 12,000 J of work on the System and Surroundings system is _______ J. Recall, when heat is absorbed Surroundings by the system from the A -24000 surroundings, the process is System endothermic . B -12000 Surroundings C 0 -q Heat D System +12000 E +24000 +q Heat When heat is released by the system into the surroundings, the process is exothermic. Slide 27 / 118 Slide 28 / 118 12 What will happen when a hot rock is put into 11 The reaction that occurs inside the foot warmer packet is cold water? endothermic? A the water and rock will both gain energy True B the water and rock will both lose False energy C the rock will gain energy and the water will lose energy D the rock will lose energy and the water will gain energy Slide 29 / 118 Slide 30 / 118 13 If you put a hot rock in cold water, and your 14 If you put a hot rock in cold water, and your system is the rock, the process is _______. system is the water, the process is _______. A exothermic A exothermic B B endothermic endothermic C neither, there is no net change of energy C neither, there is no net change of energy D it depends on the exact temperatures D it depends on the exact temperatures
Slide 31 / 118 Slide 32 / 118 15 If you put an ice cube in water, and your system 16 If you put an ice cube in water, and your system is the ice, the process is _______. is the water, the process is _______. A exothermic A exothermic B endothermic B endothermic C neither, there is no net change of energy C neither, there is no net change of energy D it depends on the exact D it depends on the exact temperatures temperatures Slide 33 / 118 Slide 34 / 118 17 When NaOH dissolves in water, the temperature of 18 When CaCl 2 dissolves in water the temperature of solution increases. This reaction is________. water drops. This reaction is _____. A exothermic A endothermic B endothermic B exothermic Slide 35 / 118 Slide 36 / 118 19 Water droplets evaporating from the skin surface will make you feel cold. This process is _____. State Functions** A exothermic for water B endothermic for skin C exothermic for skin D endothermic for water E A and C Return to Table of F C and D Contents
Recommend
More recommend
