Question

Calcium reacts with HCl according to the following reaction: Ca(s) + 2HCl(aq) -> CaCl2(aq) + H2(g) If the reaction of 2.5 g of Ca transfers 487 J of heat to a solution in a calorimeter (i.e. qsoln = + 487 J), determine Δ H r x n . Report your answer with units of kJ/mol. If you number is negative, include the negative symbol. If your number is positive, do not include the positive symbol.

Answer 1

The enthalpy change for the reaction of calcium with hydrochloric acid, given that 2.5 g of Ca transfers 487 J of heat to the solution, is ΔHrxn = -7.809 kJ/mol.

Step-by-step explanation:

To calculate the enthalpy change (ΔHrxn) for the reaction of calcium with hydrochloric acid (HCl), we need to know the amount (in moles) of calcium that reacted and the amount of heat transferred. Given that 2.5 g of Ca reacts and transfers 487 J of heat, we first convert the mass of calcium to moles:

Molar mass of Ca = 40.08 g/mol

Moles of Ca = 2.5 g ÷ 40.08 g/mol = 0.0624 mol

The reaction is: Ca(s) + 2HCl(aq) → CaCl2(aq) + H2(g)

Since the reaction involves one mole of Ca reacting to produce heat, we use the heat transferred and the moles of Ca to find the enthalpy change per mole:

qsoln = +487 J

ΔHrxn = qsoln ÷ moles of Ca

ΔHrxn = +487 J ÷ 0.0624 mol = +7809.29 J/mol ≈ 7.809 kJ/mol

Since the heat is transferred to the solution, the reaction is exothermic, and therefore the enthalpy change should be negative:

ΔHrxn = -7.809 kJ/mol.