Medical cold packs can use various chemicals in order to produce a cold compress to help reduce inflammation caused by injuries. Based on the accepted value in Question 1, how many grams of potassium chloride would have to be dissolved into 750 g of 20.0°C water to produce a 4.0°C solution? (Remember: specific heat of water is 4184 J/g·°C) 92 4.

We need 217.7 grams of KCl

Explanation:

Medical cold packs can use various chemicals in order to produce a cold compress to help reduce inflammation caused by injuries. Based on the accepted value of 17.2 kJ/mol, how many grams of potassium chloride would have to be dissolved into 750 g of 20.0 degree Celsius water to produce a 4.0 degree Celsius solution?

Step 1: Data given

Mass of water = 750 grams

Temperature = 20.0 °C

Temperature of the solution = 4.0 °C

Specific heat of water 4.184 J/g°C

Step 2: Calculate the heat

Q = m* c * ΔT

⇒with Q = the heat transfer = TO BE DETERMINED

⇒with m = the mass of water = 750 grams

⇒with c = the specific heat of water = 4.184 J/g°C

⇒with ΔT = The change of temperature = 16 °C

Q = 750 * 4.184 * 16

Q = 50208 J = 50.2 kJ

Step 3: Calculate moles KCl

Moles KCl = 50.2 kJ / 17.2 kJ/mol

Moles KCl = 2.92 moles

Step 4: Calculate mass KCl

Mass KCl = moles KCl * molar mass KCl

Mass KCl = 2.92 moles * 74.55 g/mol

Mass KCl = 217.7 grams

We need 217.7 grams of KCl

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