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 nitrate dissolves according to the following endothermic reaction: NH4NO3(s)>NH+4(aq)+NO-3(aq) In order to measure the enthalpy change for this reaction, 1.25 g of NH4NO3 is dissolved in enough water to make 25.0 mL of solution. The initial temperature is 25.8 degree C and the final temperature (after the solid dissolves) is 21.9 degree C.

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

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

The enthalpy change of the reaction is -27. kJ/mol

Explanation:

To calculate the mass of water, we use the equation:

Density of water = 1 g/mL

Volume of water = 25.0 mL

Putting values in above equation, we get:

To calculate the heat released by the reaction, we use the equation:

where,

q = heat released

m = Total mass = [1.25 + 25] = 26.25 g

c = heat capacity of water = 4.18 J/g°C

= change in temperature =

Putting values in above equation, we get:

To calculate the number of moles, we use the equation:

Given mass of ammonium nitrate = 1.25 g

Molar mass of ammonium nitrate = 80 g/mol

Putting values in above equation, we get:

To calculate the enthalpy change of the reaction, we use the equation:

where,

q = amount of heat released = -0.428 kJ

n = number of moles = 0.0156 moles

= enthalpy change of the reaction

Putting values in above equation, we get:

Hence, the enthalpy change of the reaction is -27. kJ/mol

the answer to your question is c.

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