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Determining The Enthalpy Change for the Reaction Between Copper Sulfate and Zinc
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IB Chemistry Lab Report
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Determining The Enthalpy Change for the Reaction BetweenCopper Sulfate and Zinc
I. INTRODUCTION
Enthalpy (H or ΔH) is a thermodynamic quantity equivalent to the total heat content of a
system. It is a state function independent of the pathway between initial and final
measurements; only the initial and final temperature of a reaction matter. The unit for
enthalpy change (ΔH) is kJ/mol, usually expressed under standard conditions. The
enthalpy change for a chemical reaction gives us an idea of the thermodynamics of this
reaction, helping us to determine whether it is exothermic or endothermic. A negative
value for enthalpy change means the reaction was exothermic (the system is losing
heat), while a positive value means it was endothermic (the system - reactants of the
reaction - are gaining heat). Enthalpy is calculated using the formula -Q/mol, where Q is
the amount of energy transferred in the chemical reaction. Q is obtained through the
formula Q=mcΔT, and the denominator is the number of moles of the limiting reagent in
the reaction.
In this lab experiment, we will be determining the enthalpy change for the single
displacement redox reaction between zinc and copper (II) sulphate. The first step is to
plot a graph of time against temperature, which will be measured using a data logger.
Then Q is calculated using the temperature change value from the graph. The value of
Q is then used to obtain ΔH. To ensure that minimum heat is lost from the reaction
vessel to the surroundings, the beaker where the reactants are mixed will be insulated
using insulating material.
Balanced chemical equation for the reaction:
Zn (s) + CuSO4 (aq) --> Cu (s) + ZnSO4 (aq)
II. METHODOLOGY
Variables
The independent variables for this experiment are the concentration and volume of
Copper (II) Sulphate solution used and the mass of Zinc powder used.
The dependent variables are the enthalpy change of the reaction and the change in
temperature every 30 seconds.
, Here are the controlled variables and how we controlled them:
Variable How it was controlled
Room temperature Keeping the air conditioner at the same
temperature throughout
Heat inside reaction vessel To minimize heat losses during the reaction, the
beaker was insulated with fleece which was
wrapped around it, and a polystyrene lid, which
was cut out from a polystyrene cup.
Pressure A constant pressure was maintained by using the
same apparatus for each trial, so that the enthalpy
value can be calculated at “standard conditions”.
Time The time that the Zinc and Copper (II) Sulphate
were allowed to react was the same for each trial.
Materials
Fleece Glass stirring rod Tape
Polysterene cup Scissors 50 mL beaker
Data logger + sensor Analytical Digital Balance
0.2 M Copper (II) Sulphate Spatula
solution
Zinc powder Filter paper
Procedure
1. Cut out a generous amount of fleece and wrap it around the beaker, setting it in
place with tape.
2. Make two holes inside the polystyrene cup using the scissors (one for the stirring
rod and one for the data logger sensor).
3. Measure the mass of the filter paper using the digital balance and tar it.
4. Measure out 1.2 grams of Zinc powder using the balance. Place the Zinc powder
on the filter paper.
5. Calibrate the data logger.
6. Place 50 mL of 0.2 M Copper (II) Sulphate solution inside the beaker and
immediately cover it with the cup.
7. Place the sensor inside one of the holes and start measuring the temperature using
the data logger.
8. Measure at 30 second intervals for 2.5 minutes.
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