## Wednesday, October 13, 2010

### We could do this on our lab but i don't think we have this calorimeter :]

 Calorimetry
 Calorimetry is used to determine the heat released or absorbed in a chemical reaction. The calorimeters shown here can determine the heat of a solution reaction at constant (atmospheric) pressure. The calorimeter is a double styrofoam cup fitted with a plastic top in which there is a hole for a thermometer. (It's crude, but very effective!) Key techniques for obtaining accurate results are starting with a dry calorimeter, measuring solution volumes precisely, and determining change in temperature accurately.
 Using a Calorimeter
 Solutions volumes should be carefully measured with a graduated cylinder. Add solution completely, to a drycalorimeter. Don't forget to add the spin bar each time!
 Set up the calorimeter with the thermometer (0° to 50°C, graduated every 0.1°C) supported from a stand so that the bulb does not touch the bottom of the cup. Note that the thermometer used for calorimetry differs from the less accurate one in your glassware drawer. Clamp the calorimeter so that it rests on the stirrer. Be careful not to turn on the heat or you will melt the styrofoam.
 The change in temperature is determined by measuring the initial temperature, T1, of the reactants, and the maximum temperature, T2, of the contents of the calorimeter during the exothermic reaction. Use a magnifying glass to measure temperature values precisely.
 Interpolate between the divisions of the themometer and record temperatures to +/- 0.01 °C. See your lab manual for a discussion of how to determine accurately the change in temperature from your graph of temperature vs. time.

source: http://www.dartmouth.edu/~chemlab/techniques/calorimeter.html#top

## Thursday, October 7, 2010

### What is Calorimetry?

Calorimetry

Calorimetry is the science of measuring heat of chemical reaction or physical changes. Calorimetry is performed with a calorimeter.The word Calorimetry is derived from the latin word "calor", meaning heat. Scottish physician and scientist Joseph Black was the founder of calorimetry.

Calorimetry has two kinds, the indirect calorimetry and direct calorimetry. Indirect calorimetry calculates heat that  living organism produce from their production of carbon dioxide and nitrogen waste while direct calorimetry it also calculates the heat that living organism produce in which the entire organism is placed inside the calorimeter for the measurement.

Calorimeter

Calorimeter is a device used for calorimetry, the science of measuring the heat of chemical reaction or physical change as well as heat capacity. There are many types of calorimeter, some of this are scanning calorimeters, isothermal micro calorimeters, titration calorimeters and accelerated calorimeter. A simple calorimeter just consist of a thermometer attached to a metal container full of water suspended above the combustion chamber.

Specific Heat

The specific heat is the amount of heat per unit mass required to raise the temperature by one degree Celsius. The relationship between heat and temperature change is usually expressed in the form shown below where c is the specific heat. The relationship does not apply if a phase change is encountered, because the heat added or removed during a phase change does not change the temperature.

Equation:

The specific heat of water is 1 calorie/gram °C = 4.186 joule/gram °C which is higher than any other common substance. As a result, water plays a very important role in temperature regulation. The specific heat per gram for water is much higher than that for a metal.

On Heat Capacity:

• The Heat Capacity itself is extensive (scales with the size of system), but we can think of making this quantity intensive (making it an intrinsic property of the material) by defining related quantities:
• the Molar Heat Capacity is defined as the Heat Capacity of a homogeneous pure compound (or element) divided by the the number of moles of that compound (or element)
• the Specific Heat is defined as the Heat Cpacity of a homogeneous sample divided by its mass.
• The Heat Capacity of any substance is positive.
• The Heat Capacity is discontinuous at phase transitions.
• For a gas, the Heat capacity depends on how one does the heating. The Heat Capacity at constant Volume, CV, and the Heat Capacity at constant pressure, Cp, for any given substance are are almost exactly equal if the substance is a solid or a liquid.  This means that for a liquid or a solid, the heat capacity doesn't depend on how you perform the heating. Cp and CV are not equal for a gas;  Cp is always greater than CV by a constant value. For one mole of gas, the difference between Cp and CV is the constant R (R is the so called universal gas constant)  and represents the capacity of the gas to perform expansion work at constant applied pressure. {Cp = CV+R for an ideal gas}  Since, for solids and liquids, the constant pressure and constant volume Heat Capacities are the same, the subscript p or V on the 'C' is usually dropped.
• Q = m C DT This means that the proportionality between the Heat flow into (or out of) an object and the Temperature change of that object is the total Heat Capacity, which can be expressed as a molar property or per mass.
• if m is moles and C is molar Heat Capacity
• if m is mass (grams) and C is the Specific Heat
• Q is positive for a temperature increase because the system has undergone an endothermic change of state

Note: The molar heat capacities of most metals around room temperature are all around 25 J/K.g. This is because the capacity to accommodate energy depends on the number of metal atoms. Non-metals are a little more complicated