Calorimetry thermodynamics general chemistry.pptx

Calorimetry thermodynamics general chemistry.pptx

1. Thermochemistry: Calorimetry

2. CALORIMETRY The measure of the flow of energy (as heat) between the system and its surroundings.

3. To calculate Calorimetry (experimentally), the equation below is used. q = C ∆ t ∆ t=   Where: q =heat C =heat capacity ∆ t = change in temperature m =mass C =specific heat(constant) C=mc

4. Heat capacity (C) Is the amount of energy needed to increase the temperature of the material by 1⁰C The unit of heat capacity is J/⁰C The heat capacity of a substance can only be determined experimentally through calorimetry. For pure substances, to get the heat capacity, this formula is used; C=mc Where: m =mass of substance in grams c =specific heat

5. Specific heat is the amount of energy needed to increase the temperature of one gram of the substance by 1⁰C . The specific heat of a substance is constant

6. Calorimeter An insulator apparatus that contains water or any liquid of known heat capacity.

7. In calorimetry, the system of interest can be a substance (for which heat of solution or heat of dissociation is measured) or any chemical reaction (for which heat of reaction or heat of neutralization is measured). The system exchanges heat with the water and the components of the calorimeter.

8. In some cases, the calorimeter is an excellent insulator and absorbs only a negligible amount of heat. Thus, the system is assumed to exchange heat only with the water in the calorimeter. To calculate the following ( heat of reaction, heat of neutralization, heat of solution or heat of dissociation ) the formula below is used;  

9. Sample problem: How much heat is absorbed by liquid water that weighs 550 grams as it is heated from 25⁰C to 95⁰C?

10. Sample problem: How much heat is released by a 76-gram piece of copper as it cools from 450 ⁰C to 28 ⁰C ?

11. Sample problem: The heat solution of a solid sample was determined using a coffee cup calorimeter that contains 250 ml of water initially at 25 ⁰C . As the sample is dissolved in the water, the temperature of the water decreased to 110 ⁰C . What is the heat of solution of the sample? Assume that the density of the water is 1 g/ml and that the coffee cup is a good insulator. Is the process endothermic or exothermic?

12. Sample problem: The heat of neutralization between an acid and a base was determined using a coffee cup calorimeter with negligible contribution to the heat capacity. The aqueous solutions of the acid and base both registered an initial temperature of 28 ⁰C . Following the calorimetric procedure, 100 ml each of the two solutions with the same concentration were mixed in the calorimeter. After mixing, the temperature increased to 34.6 ⁰C . Assuming that the total volume of the mixture is also the volume of the water in the calorimeter and that the density of water is 1 g/ml, calculate the heat of neutralization of the process.