Enthelpy Change of Reaction

In summary, the conversation discusses a chemical reaction between Zn and Cu2+ in a polystyrene cup. The enthalpy change for the reaction is calculated using the mass of Zn and CuSO4, as well as the change in temperature of the solution over 6 and a half minutes. The enthalpy change for one mole of Zn and CuSO4 is also calculated and the thermochemical equation for the reaction is written. Further calculations are needed to determine the limiting reactant.
  • #1
mgnymph
15
0

Homework Statement



Zn(solid) + Cu2+(aq) -> Cu(solid) + Zn2+(aqueous)
5.96grams on zinc was added to 25cm^3 of 1M copper(II)sulphate solution in a polystyrene cup.
Over 6 and a half minutes, the temperature of the solution decreased from 68 degrees Celsius to 19.5 degrees C.

1. Calculate enthalpy change for the quantities used, making appropriate assumptions
2. Calculate the enthalpy change for one mole of Zn and CuSO4(aq) and write the thermochemical equation for the reaction

2. The attempt at a solution

1.
moles of Zn = 5.96/65.4 = 0.09113... or 149/1635
therefore, moles of Cu2+ in CuSO4 = 149/1635 (because ratio in above equation is 1 to 1


mass of CuSO4 in solution = 149/1635 x molar mass of CuSO4 = 14.54 grams

q = mcDT,
m = 25 grams, c = 4.2, DT = 68-19.5 = 48.5
q = 5092.5 joules

DH = q/n
= 5092.5/(149/1635)
= 55880Jmol^-1

temperature increased so enthalpy is negative
-> -55880joules per mol

2. Zn + Cu2+ -> Zn2+ + Cu DH = -55880 joules



I'm not sure if I'm doing this right...
 
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  • #2
mgnymph said:
2. The attempt at a solution

1.
moles of Zn = 5.96/65.4 = 0.09113... or 149/1635
therefore, moles of Cu2+ in CuSO4 = 149/1635 (because ratio in above equation is 1 to 1

For the moles of Cu2+, you'll need to use the information given about the copper(II)sulphate solution. It's not necessarily the same # of moles as the Zinc ... either Cu or Zn will be the limiting reactant here.

Other than that, your methods look fine.
 
  • #3


Your calculations for the enthalpy change appear to be correct. The negative sign indicates that the reaction is exothermic, meaning that it releases energy. This is consistent with the decrease in temperature observed during the reaction.

In terms of the thermochemical equation, it would be written as:

Zn(s) + Cu2+(aq) -> Zn2+(aq) + Cu(s) DH = -55.88 kJ/mol

Note that the enthalpy change is typically reported in kilojoules per mole (kJ/mol) rather than joules per mole (J/mol).

Additionally, the polystyrene cup may have affected the reaction by insulating the solution and preventing heat from escaping. This could have resulted in a slightly lower enthalpy change than the actual value. It is also important to consider any sources of error in the experiment, such as measurement errors or incomplete mixing of the reactants. Overall, the enthalpy change calculated from this experiment may not be entirely accurate, but it can still provide a general understanding of the energy involved in this reaction.
 

1. What is entropy change of reaction?

Entropy change of reaction is a measure of the change in the degree of disorder or randomness in a chemical reaction. It is a thermodynamic property that indicates the tendency of a reaction to occur spontaneously.

2. How is entropy change of reaction calculated?

Entropy change of reaction can be calculated using the formula ΔS = ΣnS(products) - ΣmS(reactants), where n and m represent the coefficients of the products and reactants, respectively, and S is the molar entropy of each substance.

3. What factors affect entropy change of reaction?

The main factors that affect entropy change of reaction are the number of moles of reactants and products, the physical state of the reactants and products, and the temperature of the reaction.

4. How does entropy change of reaction relate to spontaneity?

Entropy change of reaction is closely related to spontaneity. A positive ΔS indicates an increase in disorder, which is favorable for spontaneous reactions. On the other hand, a negative ΔS indicates a decrease in disorder, which is unfavorable for spontaneous reactions.

5. Can entropy change of reaction be negative?

Yes, entropy change of reaction can be negative. This indicates a decrease in disorder or randomness in a reaction, which is generally unfavorable and requires an input of energy to occur. However, a negative entropy change of reaction does not necessarily mean that the reaction will not occur, as other factors such as enthalpy change also play a role in determining the spontaneity of a reaction.

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