EXPERIMENT 5 Thermochemistry : Specific Heat of a Metal

Temperature Changes: Heat Capacity Heat Capacity : The quantity of heat (usually in joules) required to change the temperature of a given amount of the substance by 1 °C (also in Kelvin). Specific Heat Capacity : When the amount of the substance is expressed in grams, the heat capacity is called the specific heat capacity (or the specific heat) and has units of joules per gram per degree Celsius, J/g °C (also in Kelvin) Remember 1 calorie = Joules ( J )

Lists the values of the specific heat capacity for several substances. Notice that water has the highest specific heat capacity on the list. This table is useful when solving homework problems.

Energy and Heat Capacity Calculations q = is the amount of heat in joules. m = is the mass of the substance in grams. C = is the specific heat capacity in joules per gram per degree Celsius. T = is the temperature change in Celsius. The symbol Δ means the change in, so ΔT means the change in temperature. The equation that relates these quantities is ONLY VALID IF HEATING/COOLING A LIQUID/SOLID OR GAS PHASE ONLY!

Relating Heat Energy to Temperature Changes Gallium is a solid at 25.0 °C but melts at 29.9 °C. If you hold gallium in your hand, it melts from your body heat. How much heat must 2.5 g of gallium absorb from your hand to raise its temperature from 25.0 °C to 29.9 °C? The specific heat capacity of gallium is J/g °C. Given: 2.5 g gallium (m) T i = 25.0 °C T f = 29.9 °C C = J/g°C = Find: q Solution Map Relationships Used q = m  C  ΔT

Relating Heat Energy to Temperature Changes Gallium is a solid at 25.0 °C but melts at 29.9 °C. An additional 200 J would be needed to melt 2.5 g of gallium once it reaches the melting point. ΔH fus =5.59 kJ/mol. If 1 calorie = Joules, then :- specific heat capacity of gallium will be 4.6J ÷ = = 1.1 calories

 1 calorie is the amount of heat required to raise the temperature of one gram of water by 1 0 C.  If : - q = 1 calorie m = 1 gram. C = ? Δ T = 1 0 C Then the Specific heat capacity of water, C = 1 cal/g 0 C BRITISH THERMAL UNIT (BTU)  Is the amount of heat required to raise the temperature of 1 pound of water by 1 0 Fahrenheit.  If : - q = 1 BTU m = 1 lb. C = ? Δ T = 1 0 F Then the Specific heat capacity of water, C = 1 BTU/lb 0 F CALORIE

LAW OF DULONG - PETIT  The equation is used to determine if the value obtained from the laboratory experiment is approximately correct.  Applies for elements of the periodic table with a molecular weight greater than 40 g/mol  Used to determine the % error (must use a known specific heat capacity given in the reference book or trusted online sources)

Heat lost!!

ISOLATED AND CLOSED SYSTEMS

So, Qw + Qcu = 0 ( LAW OF CONSERVATION OF ENERGY)

THE METHOD OF MIXTURES

Now applying the Law of Dulong – Petit to check for accuracy and determine metal identity….

ISOLATED AND CLOSED SYSTEMS EXPERIMENTAL SET- UP