2 Measuring and Expressing Enthalpy Changes 17.2A burning match releases heat to its surroundings in all directions. How much heat does this exothermic reaction release? You will learn to measure heat flow in chemical and physical processes by applying the concept of specific heat.
3 17.2CalorimetryCalorimetryWhat basic concepts apply to calorimetry?
4 17.2CalorimetryCalorimetry is the precise measurement of the heat flow into or out of a system for chemical and physical processes.
5 17.2CalorimetryIn calorimetry, the heat released by the system is equal to the heat absorbed by its surroundings. Conversely, the heat absorbed by a system is equal to the heat released by its surroundings.
6 17.2CalorimetryThe insulated device used to measure the absorption or release of heat in chemical or physical processes is called a calorimeter.In a simple constant-pressure calorimeter, a thermometer records the temperature change as chemicals react in water. The substances reacting in solution constitute the system. The water constitutes the surroundings.
7 Constant-Pressure Calorimeters 17.2CalorimetryConstant-Pressure CalorimetersThe heat content of a system at constant pressure is the same as a property called the enthalpy (H) of the system.
8 Constant-Volume Calorimeters 17.2CalorimetryConstant-Volume CalorimetersCalorimetry experiments can be performed at a constant volume using a bomb calorimeter.Nutritionists use bomb calorimeters to measure the energy content of the foods you eat. To see some of their data (expressed in Calories per serving), you can look at a nutrition label. Calculating According to the nutrition label below, each serving contains 140 Calories. How many kilojoules is this?
13 for Sample Problem 17.2Problem Solving Solve Problem 13 with the help of an interactive guided tutorial.
14 Thermochemical Equations 17.2Thermochemical EquationsThermochemical EquationsHow can you express the enthalpy change for a reaction in a chemical equation?
15 Thermochemical Equations 17.2Thermochemical EquationsIn a chemical equation, the enthalpy change for the reaction can be written as either a reactant or a product.
16 Thermochemical Equations 17.2Thermochemical EquationsA chemical equation that includes the enthalpy change is called a thermochemical equation.
17 Thermochemical Equations 17.2Thermochemical EquationsThe heat of reaction is the enthalpy change for the chemical equation exactly as it is written.
18 Thermochemical Equations 17.2Thermochemical EquationsExothermic ReactionThese enthalpy diagrams show exothermic and endothermic processes: a) the reaction of calcium oxide and water and b) the decomposition of sodium bicarbonate. Identifying In which case is the enthalpy of the reactant(s) higher than that of the product(s)?
19 Thermochemical Equations 17.2Thermochemical EquationsEndothermic ReactionThese enthalpy diagrams show exothermic and endothermic processes: a) the reaction of calcium oxide and water and b) the decomposition of sodium bicarbonate. Identifying In which case is the enthalpy of the reactant(s) higher than that of the product(s)?
20 Thermochemical Equations Simulation 22Simulate a combustion reaction and compare the ∆H results for several compounds.
27 Thermochemical Equations 17.2Thermochemical EquationsThe heat of combustion is the heat of reaction for the complete burning of one mole of a substance.The combustion of natural gas is an exothermic reaction. As bonds in methane (the main component of natural gas) and oxygen are broken and bonds in carbon dioxide and water are formed, large amounts of energy are released.
29 the enthalpy change of the reaction in the calorimeter. 17.2 Section Quiz.1. The change in temperature recorded by the thermometer in a calorimeter is a measurement ofthe enthalpy change of the reaction in the calorimeter.the specific heat of each compound in a calorimeter.the physical states of the reactants in a colorimeter.the heat of combustion for one substance in a calorimeter.
30 17.2 Section Quiz.2. For the reaction CaO(s) + H2O(l) Ca(OH)2(s), H = 65.2 kJ. This means that 62.5 kJ of heat is __________ during the process.absorbeddestroyedchanged to massreleased
31 17.2 Section Quiz.3. How much heat is absorbed by 325 g of water if its temperature changes from 17.0°C to 43.5°C? The specific heat of water is J/g°C.2.00 kJ3.60 kJ36.0 kJ360 kJ
32 17.2 Section Quiz.4. Which of the following is a thermochemical equation for an endothermic reaction?CH4(g) + 2O2(g) CO2(g) + 2H2O(g) kJ241.8 kJ + 2H2O(l) 2H2(g) + O2(g)CaO(s) + H2O(l) Ca(OH)2(s) kJ2NaHCO3(s) 129 kJ Na2CO3(s) + H2O(g) + CO2(g)
33 17.2 Section Quiz.5. Oxygen is necessary for releasing energy from glucose in organisms. How many kJ of heat are produced when 2.24 mol glucose reacts with an excess of oxygen?C6H12O6(s) + 6O2(g) 6CO2(g) + 6H2O(g) kJ/mol4.66 kJ9.31 kJ1048 kJ6290 kJ