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Multiple Choice
When 8.00 g of Ba (s) is added to 100.00 g of water in a container open to the atmosphere, the reaction shown occurs and the temperature of the resulting solution rises from 22.0°C to 77.62°C. If the specific heat of the solution is 4.18 J/(g°C), calculate ΔH for the reaction. Assume no heat is lost to the surroundings.
A
-50.0 kJ
B
-33.5 kJ
C
-25.5 kJ
D
-40.0 kJ
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1
Identify the chemical reaction: Ba(s) + 2H2O(l) → Ba(OH)2(aq) + H2(g). This is an exothermic reaction where barium reacts with water to form barium hydroxide and hydrogen gas.
Calculate the total mass of the solution. Since 8.00 g of Ba is added to 100.00 g of water, the total mass of the solution is 108.00 g.
Determine the heat absorbed by the solution using the formula q = m × c × ΔT, where m is the mass of the solution, c is the specific heat capacity, and ΔT is the change in temperature. Here, m = 108.00 g, c = 4.18 J/(g°C), and ΔT = 77.62°C - 22.0°C.
Convert the heat absorbed (q) from joules to kilojoules by dividing by 1000, since ΔH is typically expressed in kJ.
Since the reaction is exothermic, the heat absorbed by the solution is equal to the negative of the enthalpy change of the reaction (ΔH). Therefore, ΔH = -q (in kJ).