Chapter 16: Energy and Chemical Change Table of Contents Chapter 16: Energy and Chemical Change 16.1: Energy 16.2: Heat in Chemical Reactions and Processes 16.3: Thermochemistry 16.3: Thermochemical Equations 16.4: Calculating Enthalpy Change

universe = system + surroundings Energy and Chemical Change: Basic Concepts Chemical Energy and the Universe universe = system + surroundings The Universe is everything around us the System: the specific part of the universe that you are studying. the Surroundings: everything else

Energy is the ability to do work or produce heat. Energy and Chemical Change: Basic Concepts The Nature of Energy Energy is the ability to do work or produce heat. Potential energy: stored energy. Kinetic energy: the energy of movement.

Chemical potential energy: stored in bonds Energy and Chemical Change: Basic Concepts The Nature of Energy Chemical potential energy: stored in bonds The energy stored in a substance because of its composition : the type of atoms in the substance the number and type of chemical bonds joining the atoms the way atoms are arranged.

Molecular kinetic energy: Measure of molecular “speed” Energy and Chemical Change: Basic Concepts The Nature of Energy Molecular kinetic energy: Measure of molecular “speed” Measured by a thermometer: As temperature increases, the motion of submicroscopic particles increases. So a thermometer is like a molecular speedometer.

Chemical systems contain both kinetic energy and potential energy. Energy and Chemical Change: Basic Concepts The Nature of Energy Chemical systems contain both kinetic energy and potential energy. Law of conservation of energy: energy can be converted from one form to another, but it is neither created nor destroyed. suppose you have money in two accounts at a bank and you transfer funds from one account to the other. Although the amount of money in each account has changed, the total amount of your money in the bank remains the same. the first law of thermodynamics

Chemical potential energy Energy and Chemical Change: Basic Concepts Chemical potential energy Heat (symbol=q), is the flow of kinetic energy due to temperature changes. Exothermic = gives off heat (hot) Forming bonds – releases energy Endothermic = takes in heat (cold) Breaking bonds – requires energy Heat always travels from hot to cold.

1,000 calories = 1 kilocal = 1 Calorie Energy and Chemical Change: Basic Concepts Measuring heat UNITS calorie (cal): metric unit of energy the amount of energy required to raise the 1 gram of water 1° Celsius 1,000 calories = 1 kilocal = 1 Calorie dietary Calories chemistry calories

joule (J): The SI unit of heat and energy Energy and Chemical Change: Basic Concepts Measuring heat UNITS joule (J): The SI unit of heat and energy 4.184 joules = 1 calorie 1,000 J = 1 kJ (Calories are bigger than joules)

Converting Energy Units Steps for converting units: Energy and Chemical Change: Basic Concepts Converting Energy Units Steps for converting units: 1. Find your goal 2. Start with what you know 3. Use conversion factors to change units 4. Check that units cancel

Converting Energy Units Ex1) How much energy in joules is 270 nutritional Calories? Goal = Joules Known = 270 Calories J = 270 Cal 1000 cal 4.184 J = J 1,129,680 1 Cal 1 cal = 1.1 x 106 J convert Cal to cal convert cal to J How much is that? Combustion of 1 mol methane is the less than the energy that you get from this clif bar. It’s WOW!

Practice converting energy units Ex2) Convert 142 Nutritional Calories into calories. Ex3) An exothermal reaction releases 86.5 kJ. How many kilocalories of energy are released? Ex 4) If an endothermic process absorbs 256 J, how many kilocalories are absorbed? 142,000 cal 20.7 kcal 0.0612 kcal

used to determine the specific heat of unknown metals Energy and Chemical Change: Basic Concepts Measuring Heat Calorimeter: a device used to measure the amount of heat absorbed or released during a chemical or physical process. used to determine the specific heat of unknown metals

Each substance has its own specific heat. Energy and Chemical Change: Basic Concepts Specific Heat The specific heat (c): the amount of heat required to raise the temperature of 1 gram of any substance by 1° C. Each substance has its own specific heat. Why? Because different substances have different compositions. specific heat (c) of water = 4.184 J/(g∙°C)

∆T = |Tfinal – Tinitial| Energy and Chemical Change: Basic Concepts Calculating heat evolved and absorbed Heat absorbed or released by a substance during a change in temperature: specific heat (J/g ·°C) mass (g) Change in temperature (°C) HEAT (J) ∆T = |Tfinal – Tinitial|

Calculating Specific Heat Energy and Chemical Change: Basic Concepts Calculating Specific Heat Ex5) The temperature of a sample of iron with a mass of 10.0 g changed from 50.4°C to 25.0°C with the release of 114 J heat. What is the specific heat of iron? q 114 J c = = = m · ΔT (10.0 g) |25.0°C-50.4°C| 114 J = = .449 J/(g·°C) (10.0 g) (25.4°C)

Using Data from Calorimetry Energy and Chemical Change: Basic Concepts Using Data from Calorimetry Ex6) A piece of metal with a mass of 4.68 g absorbs 256 J of heat when its temperature increases by 182°C. What is the specific heat of the metal? Known Unknown mass of metal = 4.68 g metal specific heat c = ? J/(g·°C) heat absorbed, q = 256 J ∆T = 182°C c = .301 J/(g·°C)

Practice specific heat equation Ex7) If the temperature of 34.4 g of ethanol increases from 25.0°C to 78.8°C, how much heat has been absorbed? Ex 8) 4.50 g of gold [c = 0.129 J/(g·°C)] absorbed 276 J of heat. If the initial temperature was 25.0°C, what was the final temperature? 4.52 x 103 J 5.00 x 102 °C

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