Instant cold packs, often used to ice athletic injuries on the field, contain ammonium nitrate...


Instant cold packs, often used to ice athletic injuries on the field, contain ammonium nitrate and water separated by a thin plastic divider When the divider is broken, the ammonium (titrate dissolves according to the following endothermic reaction:

{eq}NH_4NO_3(s)→NH_4^+(aq)+NO^-_3(aq) {/eq}

In order to measure the enthalpy change for this reaction. 1.25 of NH₄ NO₃ is dissolved in enough water to make 25.0 mL of solution. The initial temperature is 25.8 °C and the final temperature (after the solid dissolves) is 21. 9 ° C.

Part A

Calculate the change enthalpy for the reaction in kilojoules per mole (Use 1.0 g/ mL as the density of the solution and 4.18 J /g. ° C as the Specific heat capacity)

Express your answer to two significant figures and include the appropriate units.


Enthalpy is the difference in energy between the reactants and products. When the chemical bonds between a collection of atoms get rearranged (as happens during a chemical reaction), they can become something that is more or less stable than what they started off as. If they end up more stable, the excess energy they started with is released into the environment as heat (exothermicity), and if they end up less stable, then the environment's thermal energy is diminished as the reactants absorb it to create a less stable product (endothermicity).

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In this experiment, we dissolve some ammonium nitrate in water, and observe the water cool. We know how much water we have and we know the change in...

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Enthalpy: Energy Transfer in Physical and Chemical Processes


Chapter 13 / Lesson 2

When energy is transferred during a chemical reaction, it is called enthalpy. Examine the changes that happen, the relationship to energy, heat, and temperature, exothermic and endothermic processes, and physical and chemical changes during enthalpy.

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