Answer:
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