U3 S1 L2 Calculating heat change! Textbook Readings MHR pages : Temperature Change and Heat pages : Transfer of Kinetic Energy page 632: Mass and Energy Transfer page 632: Type of Substance and Energy Transfer pages : Calculating Heat Transfer pages : Heat Capacity Textbook Practice Items MHR page 631: Thought Lab page 634: items 1, 2, 3 and 4 page 636: items 6, 7, 8, 9 and 10 page 638: items 4, 5, 6 and 7 page 706: item 2 page 707: items 15 and 20

Upon completion of this lesson, you should be able to: identify and explain that energy can be exchanged between a system and its surroundings through heat gained or lost by a system. (q system = -q surroundings ) state and apply the first law of thermodynamics define joule, heat capacity and specific heat capacity identify that the amount of heat an object gains from or loses to its surroundings is a function of the nature of its matter, its temperature, and its mass perform calculations involving heat capacity and specific heat capacity

1 st Law of thermodynamics The total energy of the universe is constant. Energy can neither be created nor destroyed ∆E universe = 0 Energy can not be lost or gained but simply transferred from one body to another. (Energy can also be converted into other forms) ∆E universe = ∆E system + ∆E surroundings ∆E system = - ∆E surroundings That is; –Energy is transferred from the system to the surroundings (or vice versa)

In this course we will be focusing on heat energy. (q) q system = - q surroundings q sys = - q surr Units of Heat energy: The SI unit of heat is the Joule (J) Calorie = the energy it takes to heat 1.0 g of water 1 o C 1 Calorie = Joule 1 Cal = J

Factors Affecting Heat Transfer 1.Mass (the amount of material). When all other variables are equal, an object with higher mass can absorb or release more energy than an object of lower mass. 2.Nature of material (Depends on what it is) Heat capacity, C, is the amount of heat needed to cause a 1°C change in temperature. –It is measured in J/°C. Specific heat capacity, c, is the energy needed to change the temperature of 1 g of a substance by 1°C For example, the specific heat capacity of water is J/g°C, whereas the specific heat capacity of ethanol is 2.01 J/g°C. See page 632, table 16.1 of your MHR textbook. When all other variables are equal, a substance with higher specific heat capacity can absorb or release more energy than a substance with lower specific heat 3.Temperature change. ∆T = T final - T initial

Different masses of water

Equal masses of canola oil and water

Comparing specific heat capacities Given 1.0 g of each of the following which substance absorbs the most energy per gram. Cu FeAl H 2 0 (l) Based on this data of the three metals, which one would be best to use to make an air cooled snowmobile engine? What is the advantage of having a liquid cooled engine?

Putting it all together. q = mc∆T where; q = heat energy measured in Joules (J) m = mass measured in grams (g) c = specific heat capacity mesured in (J/g o C) ∆T = change in temperature ∆T = T final - T initial

Sign Convention a positive q value indicates that a substance (system) has absorbed heat from its surroundings (an endothermic change) a negative q value indicates that a substance (system) has released heat to its surroundings (an endothermic change) Density the density of pure 25 o C is 1.0 g/mL

Sample Exercise 1 A student is required to use 225 mL of hot water in a lab procedure. Calculate the heat change involved in raising the temperature of 225 mL of water from 20.0°C to 100.0°C

Sample Exercise g pieces of iron and aluminum are placed in a hot water bath so that they are warmed to 99.7°C. The metal samples are removed and cooled to 21.5°C. Which sample undergoes the greater heat change?

Heat capacity values are determined for specific devices or pieces of equipment that undergo heat changes. –For example a certain frying pan may be known to have a heat capacity of 1.20 kJ/°C. –You may notice that there is no mass in this value! The heat change that it undergoes as it warms up is determined by multiplying the heat capacity by its temperature change, q = C∆T Sample Exercise 3 A frying pan with a heat capacity of 1.20 kJ/°C is heated from 22°C to 198°C. Calculate the heat change.

Sample Exercise 4 Calculate the specific heat capacity of an alloy if a 15.4 g sample undergoes a heat change of 393 J when it is heated from 0.0°C to 37.6°C.

1.Calculate the heat change involved when 2.00 L of water is heated from 20.0°C to 99.7°C in an electric kettle. 2.Calculate the heat change associated with cooling a g aluminum bar from 70.0°C to 25.0°C. Is the change endothermic or exothermic? Why? (Hint: what is the sign of your answer?) 3.Calculate the heat change that occurs when mL of water is heated from 3.0°C to 95.0°C on a propane camp stove. 4.A 63.5 g sample of an unidentified metal absorbs 355 J of heat when its temperature changes by 4.56°C. a.Calculate the specific heat capacity of the metal. b.Use a table of specific heat capacity values to identify the metal. 5.Calculate the specific heat capacity of titanium if a g sample absorbs kJ as its temperature changes from 20.13°C to 41.06°C.