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Chemistry 12 Unit 1 THERMOCHEMISTRY Energy: the capacity to move matter Units: Joule (J), calorie (cal) Kinetic EnergyPotential Energy (KE) (PE) The energy of motionEnergy that is stored Thermal energy: due to kinetic energy (motion) of atoms/molecules Temperature (t): measures average kinetic energy of particles on a relative scale. Units: Celsius ( ◦ C), Kelvin (K) (Absolute zero = 0K or -273 ◦ C – no particle motion)

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Heat: a transfer of kinetic energy from a higher temperature system to a lower temperature system Thermochemistry is a study of the heat that is lost or gained during chemical reactions

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Exothermic changes: heat is given off by the system Endothermic changes: heat is taken in by the system system surroundings SystemEffect on surroundings Heat value of system EndothermicTakes in heatCools + ExothermicGives off heatWarms -

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SPECIFIC HEAT CAPACITY (C) PREDICT/OBSERVE/EXPLAIN Specific heat capacity is the amount of heat needed to raise the temperature of one gram of a substance one degree Celsius. Basically, it is the ability of a substance to store heat energy. Different substances have different specific heat capacities. Water has a relatively high specific heat capacity, meaning that is takes a lot of heat to raise the temperature of water, while metals tend to have a low heat capacity. In this experiment, the specific heat capacities of five different metals were compared. Equal weights of the metals were heated until all reached the same temperature. Each metal was then placed on a block of paraffin wax and allowed to cool. During cooling, heat energy is transferred from the metal to the block of wax, melting the wax and imbedding the metals into the block.

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1. Which metal do you predict will melt the most wax and why? 2. Which metal do you predict will melt the least wax and why?

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3. List the metals in order of depth in the wax. (from most deep to least deep) 4. How does the specific heat capacity of a metal relate to the amount of wax it will melt while cooling?

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5. Daryl and Cheri each designed a frying pan. They had to choose which metal to use. Daryl wanted his pan to reach a high temperature with the least amount of heat applied. Cheri wanted her pan to stay at a high temperature even when the heat was turned low. Which metal listed in the table would be best for Daryl, and which metal would be best for Cheri? Give reasons for your answers.

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∆t = t final - t initial

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So, using this formula we can solve for any of the four variables. Rearrange the formula to solve for: Mass (m) Specific heat capacity (c) Temperature change (∆t)

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Example 1: 60.0 g of water at 26.5 C is cooled to 9.70 C. How much heat was lost by the water?

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Example 2: 60.0 g of canola oil lost 4.0 x 10 3 J of energy, resulting in a temperature decrease from 35.0 C to 5.2 C. Calculate the specific heat capacity of the canola oil.

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Homework: 1.Heat calculations worksheet 2.Course expectations contract signed 3.Lab Safety contract signed

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Energy is transferred ◦ Exothermic – heat is released Heat exits ◦ Endothermic – heat is required or absorbed by reaction Measure energy in Joules.

Energy is transferred ◦ Exothermic – heat is released Heat exits ◦ Endothermic – heat is required or absorbed by reaction Measure energy in Joules.

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