Problem: When a 6.50-g sample of solid sodium hydroxide dissolves in 100.0 g of water in a coffee-cup calorimeter (the following Figure), the temperature rises from 21.6 oC to 37.8 oC.Calculate ΔH (in kJ/mol NaOH) for the solution processNaOH(s) → Na+(aq) + OH-(aq)Assume that the specific heat of the solution is the same as that of pure water.

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We are asked to calculate ΔH (in kJ/mol NaOH) for the solution process.


Calculate heat: 

Q = mCTQ = (100 g)(4.184 J/g°C)(37.8°C-21.6 °C)Q = (100 g)(4.184 J/g°C)(16.2 °C)Q = 6778.08 J ×1 kJ103 J

Q = 6.78 kJ


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Problem Details
When a 6.50-g sample of solid sodium hydroxide dissolves in 100.0 g of water in a coffee-cup calorimeter (the following Figure), the temperature rises from 21.6 oC to 37.8 oC.

A diagram shows two Styrofoam cups nested together.  The inside cup contains the reaction mixture in solution, and is covered by a cork stopper, through which a thermometer and glass stirrer are placed.


Calculate ΔH (in kJ/mol NaOH) for the solution process

NaOH(s) → Na+(aq) + OH-(aq)

Assume that the specific heat of the solution is the same as that of pure water.

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