2 Heat q can be defined as the flow of energy into and out of a system due to a

2 heat q can be defined as the flow of energy into

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of heat absorbed or evolved by physical and chemical processes. 2) Heat ( q ) can be defined as the flow of energy into and out of a system due to a temperature difference between the thermodynamic system and its surroundings. 3) Heat energy will flow from the region of higher temperature to the region of lower temperature until thermal equilibrium has been reached. a. At thermal equilibrium, the temperature of the two regions will be equal at any one time. 4) Heat and temperature are both measures of kinetic energy but there is an important difference. a. Heat measures total energy. b. Temperature measures the average energy. c. An example to distinguish these two terms is as follows. i. Considering a teaspoonful of boiling water versus a cup of boiling water (both at 100 o C), the cup of boiling water would be more hazardous to spill because it has more heat (total energy). 5) The formula for heat is as follows: q = s m Δ t a. q = heat, s = specific heat, m = mass, Δ t = change in temperature (t f – t i ) . i. Specific heat for water = 4.184 J/(g o C) 6) In chemical reactions, heat is often transferred from the “system” to its “surroundings,” or vice versa. a. The substance or mixture of substances under study in which a change occurs is called the thermodynamic system (or just the system.) b. The surroundings are everything around that thermodynamic system that can interact. 7)The sign of qis very important! a.If qis positive, heat is absorbed by the system.i.This process is described as endothermic.b.If qis negative, heat is released from the system.i.This process is described as exothermic. Introduction to Calorimetry : 1) A calorimeter is a device used to measure the heat absorbed or evolved during a physical or chemical change. 2) There are two types of calorimeters: a. A bomb calorimeter is an isolated metal container with a known mass and known heat capacity. Experiment #8A Barnett
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42 b. A coffee cup calorimeter is a plastic–foam cups that serves as a vessel for heat exchange. i. These cups have a very low heat capacity and the small amount of heat gained/emitted is ignored. ii. The foam is a good thermal insulator that allows very little heat to escape from the calorimeter. 3) The essential formula that governs calorimetry is as follows. a. q system = – q surroundings Introduction to Heat of Fusion : 1) The heat needed to melt 1 mole of a pure substance is called the heat of fusion and denoted as ΔH fus . 2) To melt a pure substance at its melting point requires an extra boost of energy to overcome lattice energies. 3) The heat of fusion (ΔH fus ) can be calculated. a. At constant pressure, the heat exchanged is equal to the heat of fusion: i. q p = ΔH fus . Introduction to Heat of Solution : 1) A solution is a homogeneous mixture of two or more substances, consisting of ions or molecules. 2) The solute is the dissolved substance for gases or solids in a liquid solution.
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  • Spring '19
  • Chemistry, Chemical reaction, Timothy Barnett

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