How much heat in kilojoules is evolved or absorbed in each of the following reactions?(b) Reaciton of 4.88 g of barium hydroxid eoctahydrate with ammonium chloride: Ba(OH)2·8 H2O (s) + 2 NH4Cl (s) → BaCl2(aq) + 2 NH3(aq) + 10 H2O(l) ΔH° = +80.3 kJ

Verified step by step guidance

1. Determine the molar mass of barium hydroxide octahydrate, Ba(OH)2·8H2O. Add the atomic masses of barium, oxygen, hydrogen, and water molecules accordingly.
2. Calculate the number of moles of Ba(OH)2·8H2O used in the reaction by dividing the mass of Ba(OH)2·8H2O given (4.88 g) by its molar mass.
3. Identify the stoichiometry of the reaction from the balanced chemical equation. Note that 1 mole of Ba(OH)2·8H2O reacts with 2 moles of NH4Cl.
4. Use the stoichiometry of the reaction to determine the amount of heat evolved or absorbed per mole of Ba(OH)2·8H2O reacted. Since the reaction has a ΔH° of +80.3 kJ, this is the heat change for the reaction as written for 1 mole of Ba(OH)2·8H2O.
5. Multiply the number of moles of Ba(OH)2·8H2O by the heat change per mole to find the total heat evolved or absorbed in the reaction.

Key Concepts

Thermochemistry

Thermochemistry is the study of the heat energy associated with chemical reactions and physical transformations. It involves understanding how energy is absorbed or released during these processes, often quantified in terms of enthalpy change (ΔH). In the given reaction, the positive ΔH value indicates that the reaction is endothermic, meaning it absorbs heat from the surroundings.

Molar Mass and Stoichiometry

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole. Stoichiometry involves the calculation of reactants and products in chemical reactions based on balanced equations. To determine the heat evolved or absorbed in the reaction, one must first convert the mass of barium hydroxide octahydrate into moles using its molar mass, which is essential for relating the amount of substance to the enthalpy change.

Calorimetry

Calorimetry is the measurement of heat transfer during chemical reactions or physical changes. It allows chemists to quantify the heat evolved or absorbed in a reaction by using the enthalpy change and the amount of reactants involved. In this case, knowing the ΔH° value and the moles of barium hydroxide used will enable the calculation of the total heat change in kilojoules for the reaction.