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    Experiment 4.

    Specific Heat of a Metal

    LEARNING OBJECTIVES

    The students will be able to learn

    1. The concept of conservation of energy.

    2. That heat flows from a hot object to a cold one.

    3. That metals are good conductors of heat. Metals have low specific heat; for a given energy input to a given mass, the temperature rise of metals will surpass the temperature rise of non-metals.

    BACKGROUND

    The First Law of Thermodynamics states that energy can neither be created nor destroyed; it can only be transformed to a different form of energy, e.g. in batteries, the chemical energy is converted into electrical energy and in automobile engines, where the gasoline is burned, the chemical energy is converted into kinetic energy. Basically, the energy of the Universe is a constant. The Universe is composed of a System (in this experiment, the calorimeter) and its Surroundings (everything else).

    Heat energy is measured in terms of calories or Joules. One calorie is the amount of heat energy required to increase the temperature of 1.00 gram of water by 1.00 ᵒC. Specific Heat is a physical property of a substance. It is defined as “the amount of heat energy required to increase the temperature of 1.00 g of any substance by 1.00 ᵒC. Therefore, substances with low specific heat require less heat energy to raise their temperatures.

    4.18 joules

    Specific heat of water, c o

    1.00 g 1.00 C

    The unit of the specific heat is J/(g×ᵒC). There are two parts in this experiment:

    a. Determination of the specific heat of metallic copper.

    b. Determination of the specific heat of an unknown metal.

    In Part A of these investigations, you will determine the specific heat of metallic copper. Then, in Part B, you will determine the specific heat of an unknown sample and identify it by using the specific heat value provided in the Table 1.

    You will use a calorimeter to determine the specific heat of the metal. The calorimeter (in Greek calor means heat) is a device that measures the specific heat of a metal using the temperature changes of the metal and the water (see Figure 1).

    The amount of heat energy needed to increase the temperature of an object is given by the following formula:

    Q = m × c × ΔTEq. 1

    Q = heat energy (Joules) m = mass of the metal (g)

    c = specific heat of the metal J/(g.ᵒC) ΔT

    = change in temperature (ᵒC)

    Assuming an ideal calorimeter, no heat escapes from the cup (the heat is not lost to the surroundings) and the heat is exchanged between the hot metal and the cool water:

    DRY LAB SIMULATION:

    Now, using the First Law of Thermodynamics, we will write the following expression: Heat lost by the hot metallic object = Heat gained by the water

    In this experiment, the metal will be heated in a test tube immersed in boiling water that is contained in a beaker. Then, the metal will be dropped into the calorimeter (doubled Styrofoam cups originally containing water at room temperature).

    Qlost by the metal = Qgained by the waterEq. 2 mmetal × cmetal × (Tmetal – Tfinal) = mwater × cwater × (Tfinal – Twater)Eq. 3

    where

    mmetal = mass of the metal used (grams)

    cmetal = specific heat of the metal (for copper c = 0.38 J/(g×ᵒC) Tmetal = temperature of the boiling water (100ᵒC) mwater = mass of the water in the calorimeter (grams) cwater = specific heat of water; c = 4.18 J/(g×ᵒC)

    Twater = the initial temperature of the water in the calorimeter (ᵒC)

    Tfinal = the temperature of the water and the metal in the calorimeter (ᵒC)

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