Experi CALORIMETR CHM 1045LUCHM 1046L PRE-LAB DATE 1. State Hess\'s law. tempera

Question

Experi CALORIMETR CHM 1045LUCHM 1046L PRE-LAB DATE 1. State Hess's law. temperature 00200 mop or K Cos was mixed with 30.0 ml of approximately 2M pep (a) Write a balanced equation for this reaction. ltont h2erad hhat the hear energy change ot areacuon er the tealt rose by 5.2 °C. and depend 1hein an (b) Calculate the enthaloy change (A Hi of this reaction per 4q) mole of potassium carbonate. Assume that the specific heat of the final mixture is 4.184 J/g'c, a density is 1.00 g/mL. Ox3-48 138 (c) Explain WHY the hydrochloric acid need only be about 2 Exp. 7.1

Explanation / Answer

2

a)

K2CO3 (s) + 2 HCl (aq) --> H2O + CO2 (g) + 2 KCl (aq)

b)

Density = 1 g/mL

Volume added = 30 mL

Mass of HCl added = 1 * 30 = 30 g

Total Mass of reactant = total mass of products (M)

M = 30 g + 2.76 g = 32.76 g

Cp = 4.184 J/g-K

Temperature rise, T = 5.2 °C

Heat of reaction, H = M Cp T

= 32.76 * 4.184 * 5.2 J

= 712.75 J

c)

Moles of K2CO3 added = 0.02

By stoichiometry, moles of HCl required = 2 * 0.02 = 0.04

Moles of HCl added = Volume * molarity

= 30 mL * 2 M / 1000 (mL/L) = 0.06

Amount of HCl added (0.06 moles) is slightly in excess of stoichiometric requirement of 0.04 moles.

Hence, 2 M HCl is adequate.

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