Cody Keller

Period 2

Examining Hess’s Law

Introduction

        Hess’s law is named after Germain Hess, a Swiss born Russian Scientist. Hess’s law is a law of physical chemistry used in predicting the enthalpy change and conservation of energy of chemical reactions. In particular, this law state that the total energy change for a chemical reaction is not dependant on the route the reaction takes place, assuming the initial and final conditions are the same.

Research Question

How do we find the enthalpy of the reactions NaOH + HCL → H2O + NaCl, KOH + HCL → H2O + KCl, and NH4Cl + Ba(OH)2 → NH3 + BaCl2?

Hypothesis

        Part 1

If we have 51.1 grams of NaOH mixed with 48.9 grams of HCl, then their reaction should produce -55.7 KJ/mol in an exothermic reaction, according to our theoretical math.

Part 2

If we have 7.1 grams of diluted HCl and 11.7 grams of diluted KOH, then the reaction created should produce -56.7 KJ/mol in an exothermic reaction, according to our theoretical math.

Part 3

If we have 1.5 grams of both NH4Cl and Ba(OH)2 , then the occurring reaction should produce 91.32  KJ/mol in an endothermic reaction, according to our theoretical math.

Variables

Part 1

        Independent

  • The independent variables were the amounts of reactant used (51.1 grams of NaOH and 48.9 grams of HCl), and their molarity, because although they were predetermined, they were determined by us, not given to us.

Dependent

  • The changes in temperature for the products, or the ∆enthalpy (∆H) were the dependent variables for this lab.

Control

  • The beakers, graduated cylinder, stopwatch gloves, goggles, and the times recorded were the controls for this lab.

Part 2

                        Independent

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  • The amount of reactants needed (7.1 grams of diluted HCl and 11.7 grams of diluted KOH) and the amount of water needed to dilute them into their solutions were the independent variables.

Dependent

  • The changes in temperatures needed to find the actual enthalpies to compare to our theoretical values.
  • The actual enthalpies of our reactions were also dependent variables.

Control

  • The beakers, graduated cylinder, gloves, stopwatch, water, goggles, and the time recorded.

Part 3

                Independent

  • The 1.5 grams of both reactants that we needed to manipulate in order to create a constant for the ...

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