You mix 125 mL of 0.250 M CsOH with 50.0 mL of 0.625 M HF in a coffee-cup calorimeter, and the t

You mix 125 mL of 0.250 M CsOH with 50.0 mL of 0.625 M HF in...

You mix 125 mL of 0.250 M CsOH with 50.0 mL of $0.625 \mathrm{M}$ HF in a coffee-cup calorimeter, and the temperature of both solutions rises from $21.50^{\circ} \mathrm{C}$ before mixing to $24.40^{\circ} \mathrm{C}$ after the reaction. $$ \mathrm{CsOH}(\mathrm{aq})+\mathrm{HF}(\mathrm{aq}) \rightarrow \mathrm{CsF}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\ell) $$

Key Concepts

Stoichiometry and Limiting Reactant

Stoichiometry involves the quantitative relationships between reactants and products in a chemical reaction. It is used to determine the extent of a reaction by calculating the number of moles of each reactant. The limiting reactant is the species that is completely consumed first, which determines the maximum amount of product formed and the total energy change of the reaction.

Reaction Enthalpy

Reaction enthalpy is a measure of the heat change during a chemical reaction at constant pressure. It reflects whether a reaction is exothermic (releasing heat) or endothermic (absorbing heat). Determining the reaction enthalpy involves calculating the heat exchange based on the stoichiometry of the reaction and the observed temperature change in the calorimeter.

Calorimetry

Calorimetry is the experimental technique used to measure the amount of heat transferred to or from a chemical reaction or physical process. In a calorimetric experiment, a change in temperature is observed and, using the known heat capacity of the system or solution, the corresponding heat exchange (either absorbed or released) can be calculated.

Heat Transfer and Specific Heat Capacity

This concept involves understanding how heat is transferred between a system and its surroundings, often using the equation q = mc?T, where q is the heat absorbed or released, m is the mass of the substance, c is its specific heat capacity, and ?T is the temperature change. This relationship is key in converting observed temperature changes into energy values in chemical reactions.

Transcript

00:01 If we mix 125 milliliters of 0 .250 molar cesium hydroxide with 50 milliliters of 0 .625 molar hydrofluoric acid, we will end up with the total volume of 175 milliliters, and an acid -based reaction will occur, as shown here.

00:20 As this acid -based reaction occurs, there will either be a release of heat, and we will have an exothermic reaction, or the absorption of heat, and we will have an end -o -ohermic reaction, and we will have an end -ohermic reaction.

00:30 Reaction.

00:32 Most reactions are exothermic.

00:34 This reaction is exothermic and heat is released because the temperature changes from a cooler 21 .5 degrees celsius, assuming each of these were initially at 21 .5 degrees celsius, to a warmer temperature of 24 .40 degrees celsius after they were mixed.

00:55 For all chemical reactions, in order to determine the amount of heat that is released for a particular reaction, we need to figure out how much of that reactant was consumed.

01:07 So we need to identify whether or not there is a limiting reactant.

01:11 The stoichiometry of this reaction is one to one.

01:14 If we take the volume in liters of the cesium hydroxide multiplied by its concentration, we get .0315 mole cesium hydroxide.

01:23 If we do the same thing with hydrofluoric acid, we take the 50 mil liters expressed as liters .050 liters, multiplied by its concentration, we get the exact same number of moles of hydrofluoric acid.

01:36 So each of these are consumed completely and there is no limiting reactant.

01:41 So if each is consumed completely, then we know that cesium hydroxide is consumed completely, and the amount of heat produced will be due to the consumption of 0 .0315 moles of cesium hydroxide...

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