Lab: Enthalpy and Entropy [PDF]

Lab: Enthalpy and Entropy. Purpose: To observe and measure energy changes during the formation of a solution and to desc

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Name:_______________________

Lab: Enthalpy and Entropy Purpose: To observe and measure energy changes during the formation of a solution and to describe/explain these changes in terms of entropy and enthalpy. Materials: Thermometer Beaker Plastic spoonSolid NaCl, NH4Cl, CaCl2

Water Stirring rod

Procedure: 1. Place two level spoonfuls of water in a beaker and measure the temperature (T1) of the water. Record in data table. 2. Add one level spoonful of solid NaCl to the cup. Stir gently and measure the highest or lowest temperature (T2). Record. 3. Repeat the experiment two more times using NH4Cl and CaCl2. Data Table:

(change) = final - initial

Mixture

T1

T2

T

Endothermic or Exothermic

H

S

G=

H -T S

NaCl + H2O NH4Cl + H2O CaCl2 + H2O

For the last 3 columns, just tell whether the value would be (+) or (-).

H = enthalpy = heat. If the endothermic, took in heat (H2 is higher than H1 = H that is positive number) If exothermic, lost heat (H2 is lower than H1 = H that is negative number) S = entropy = disorder. The more disorganized the system gets, the larger the entropy number (+) (Lots of order, low entropy) = solids  liquids  gases (lots of disorder, high entropy)

Analyze: When sodium dissolves in water, the ions dissociate. NaCl(s)  Na+ + ClWrite the ionic equations, similar to the one above, that describes how NH4Cl and CaCl2 each dissociate as they dissolve in water. Include heat as a reactant or product in each equation. 1.

2.

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