CHM 144 experiment 8
This lab will make use of a calorimeter to measure the amount of heat given off or absorbed by a reaction. The calorimeter needs to be well-insulated in order to obtain accurate measurements; this is why _____ polystyrene coffee cups are used.
2
In Part 2 of the experiment, you will do ___ heat studies. The device you will use to conduct these studies is a calorimeter. You will conduct ___ total trials in Part 2.
4
enthalpy in kj/mol
= -qaq/mass * molar mass of salt * 1/1000
example of dissolution of inorganic salt in water reaction
CaCl2 (s) -> Ca2+ (aq) + 2Cl- (aq)
Why was it necessary to find Tf (final temperature) using Logger Pro by extrapolating back to time = 0 seconds?
Extrapolating back to time = 0 seconds to find Tf was necessary because we had to account for heat that was lost to calorimeter. The Tf could not be measured directly because a small amount of heat is lost to the calorimeter, and the observed temperature values would never attain the value of Tf that would be reached if the insulation in the calorimeter was perfect.
heat gained or lost by a system at constant pressure
Qp
Why is it important that these reactions are run in two polystyrene cups nestled in a beaker (instead of only a beaker)?
The calorimeter must be well-insulated to obtain accurate measurements, so that no heat escapes the calorimeter. The space between the two cups serves to better insulate the solution, therefore, two cups are used. The glass beaker individually would not be a good insulator to keep heat from escaping.
specific heat capacity
amount of heat required to raise the temperature of 1 gram of the material by 1 K or 1 degree C
procedure (quantitative)
assemble calorimeter and get temp probe. transfer 100 ml of deionized water into calorimeter and stir until temp stabilizes. add 4g of assigned salt to nearest 0.001g and stir until temperature stabilizes. repeat with 8g and other sample
quantitative determination of magnitude of deltaH requires a
calorimeter
ΔE=qp+w
change in energy equation
deltaH=deltaE+PdeltaV
change in enthalpy equation at constant pressure
deltaHrxn = qrxn = -qaq
constant pressure apparatus
the reaction is
dissolution of inorganic salt in water
In an experiment, a student measured the initial temperature of 100.0 mL of water to be 22.0oC. By graphical analysis, they found Tf = 16.1oC. Based on the change in temperature, is this an exothermic or endothermic reaction?
endothermic
In thermodynamics, chemists define a system. When a reaction takes place in aqueous solution, the solvent, water, is part of the surroundings. If a reaction (system) loses heat, that heat is gained by the surroundings. If a reaction gains heat, that heat is removed from the surroundings. If the temperature of the water decreases when a reaction takes place in aqueous solution, the reaction was ____________.
endothermic
Qp>0
endothermic
H=E+PV
enthalpy equation
Part 1 of the experiment involves qualitative heat studies. You will determine if a particular reaction is endothermic or exothermic by touching the outside of the reaction test tube after a salt is dissolved in water. If the test tube gets warmer upon the dissolution of the salt, the reaction was ___.
exothermic
Part 1 of the experiment involves qualitative heat studies. You can determine if a particular reaction is endothermic or exothermic by touching the outside of the reaction test tube after a salt is dissolved in water. If the test tube gets warmer upon the dissolution of the salt, the reaction was _______ . In Part 2 of the experiment, you will do _______ heat studies. The device you will use to conduct these studies is a calorimeter.
exothermic, quantitative
In the data analysis of the quantitative studies you will graph your data using Logger Pro. The initial temperature (Ti) is the temperature at time 0 seconds. The final temperature (Tf) cannot be measured directly and must be obtained by ________________ to time zero.
extrapolating
∆H = qp where ∆H is the change in enthalpy and qp is the _____________ gained or lost by a system at constant pressure.
heat
q= Cs*m*(Tf-Ti)
heat absorbed or lost
exothermic calibration curve
increases then decreases
When carrying out a chemical reaction in aqueous solution, you can easily monitor the temperature of the water (surroundings). By noting the change in temperature (Tf - Ti), you can calculate the amount of heat (q) that was either lost or gained by the water. The equation is: q = Cs∙m∙(Tf - Ti) Where m refers to the ______ of the water, Cs represents the specific heat capacity of water, Tf is the ________ temperature, and Ti is the _______ temperature.
mass, final, initial
What is a qualitative determination of whether a reaction is endothermic or exothermic?
observing whether the temperature goes up or down during a reaction
procedure (qualitative)
place 7-8 ml deionized water in the test tube with a salt and feel whether the tube feels warm or cold
If deltaH<0,
qp is also <0, heat is lost by the system to the reaction
if deltaH<0, the reaction would
remove heat from the surroundings (endothermic)
Are the inorganic salts toxic and/or irritating to the skin in Experiment 8?
some are, but you should treat them the all the same way and avoid contact with these materials
objectives
to understand the concept of enthalpy (H) to understand how ΔH is related to temperature changes during a reaction to learn to use calorimetry to experimentally determine ΔH to learn to use thermodynamic data for practical applications.
E
internal energy of a system
enthalpy (H)
the heat content of a system
In an experiment, a student measured the initial temperature of 100.0 mL of water to be 22.0oC. By graphical analysis, they found Tf = 16.1oC. Calculate the heat absorbed or lost by the aqueous solution, qaq, in Joules (J) assuming that the specific heat capacity of water is 4.18 J/g∙oC. Answer in the correct number of significant figures and be sure to include the sign (+/-). You must answer in standard form (i.e. no scientific notation).
-2500
PdeltaV=
-w
