.:heat capacity and specific heat capacity:.

Heat capacity (usually denoted by a capital C, often with subscripts) is the measurable physical quantity that characterizes the amount of heat required to change a body's temperature by a given amount. In the International System Of Units, heat capacity is expressed in units of joules per Kelvin.

The more we heat an object, the higher it's temperature.

* the quantity of heat (q) absorbed by an object is proportional to it's temperature changes.

* q α ΔT, q= constant × ΔT

*Heat capacity is proportionally constant in the preceding equation:

heat capacity (C) = q/(ΔT) [unit: J/K]

Derived quantities that specify heat capacity as an intensive property, independent of the size of the sample, are the molar heat capacity, which is the heat capacity per mole of a pure substance, and the specific heat capacity, often called simply specific heat, which is the heat capacity per unit mass of a material.

The quantity of heat required to change the temperature of 1 gram of a substance by 1 K.

Specific heat capacity (c) = q / (mass × ΔT) [unit: J/g·K]

.:Bomb-Calorimeter:.

A bomb calorimeter is a type of constant-volume calorimeter used in measuring the heat of combustion of a particular reaction. bomb calorimeters have to withstand the large pressure within the calorimeter as the reaction is being measured. Electrical energy is used to ignite the fuel; as the fuel is burning, it will heat up the surrounding air, which expands and escapes through a tube that leads the air out of the calorimeter. When the air is escaping through the copper tube it will also heat up the water outside the tube. The temperature of the allows for calculating calorie content of the fuel.

In more recent calorimeter designs, the whole bomb,pressurized wiyh excess pure oxygen(typically at 30atm)and containing a known mass of sample(typically 1-1.5g) and a small fixed amount of water(to absorb produced acid gases),is submerged under a known volume of water(ca. 2000ml) before the charge is (again electrically) ignited.The bomb,with sample and oxygen,form a closed system-no air escapes during reaction.The energy released by combustion raises the temperature of the steel bomb,its contents, and the surrounding water jacket. The temperature change in water is then accurately measured. This temperature rise, along with a bomb factor( which is dependent on the heat capacity of the metal bombs parts) is used to calculate the energy given out by the sample burn. A small correction is made to account for electrical energy input, the burning fuse, and acid production ( by titration of he residual liquid). After the temperature rise has been measured, the excess pressure in the bomb is released.

Basically, a bomb calorimeter consist of small cup contain the sample, oxygen, a stainless steel bomb), water, a stirrer, a thermometer, dewar (to prevent heat flow from the calorimeter to the surrounding) and ignition circuit connected to the bomb.

The equation involve to find in bomb-calorimeter:

qsys = qwater + qcal +qrxn

where,

qsys= 0 as there's no heat enter or leaves environment

qwater= mcΔT

qcalorimeter= CcalΔT

Therefore;

qrxn = -(qwater + qcal)

.:Coffee-cup Calorimeter:.

Also known as constant-pressure calorimeter. It is a simpler device than the constant volume calorimeter (Bomb Calorimeter), which is used to determine the heat changes for non combustion reactions. A crude constant-pressure calorimeter can be constructed from Styrofoam coffee-cup. This device measures the heat effects of a variety of reactions, such as acid-base neutralization, as well as the heat of solution and heat of dilution. Because the pressure is constant, the heat change for the process (q_rxn) is equal to the enthalpy change (ΔH).

A constant-pressure calorimeter measures the change in enthalpy of reaction occurring in solution during which the atmospheric pressure remains constant.

The equation involved in calculation for qrxn

qsys = qsoln + qcal + qrxn

since there's no heat enter or leave from system:

qsys = 0

qrxn = -(qsoln + qcal)

Where:

qsoln = mcΔT

qcal = CcalΔT

.:Type of Calorimeter:.

There are five (5) types of calorimeter.

They are: Bomb calorimeter, Calvet-type calorimeter, constant-pressure calorimeter, differential scanning calorimeter and isothermal calorimeter.

1. Bomb Calorimeter

A bomb calorimeter is a type of constant-volume calorimeter used in measuring the heat of combustion of a particular reaction

Bomb Calorimeter

2. Calvet-type reactian

The detection is based on a three-dimensional flux meter sensor. The flux meter element consist a ring of several thermo couple in series. The corresponding thermopile of high thermal conductivity surrounds the experimental space within the calorimetric block. The radial arrangement of the thermopile guarantees an almost complete integration of the heat. This is verified by the calculation of the efficiency ratio that indicates that an average value of 94% +/- 1% of heat is transmitted through the sensor on the full range of temperature of the Calvet-type calorimeter. In this setup, the sensitivity of the calorimeter is not affected by the crucible, the type of purge gas or the flow rate. The main advantages of the setup is the increase of the experimental vessel's size and consequently the size of the sample without affecting the accuracy of the calorimetric measurement.

Calvet-type Calorimeter

3. Constant-pressure calorimeter

A constant-pressure calorimeter measures the change in enthalpy of a reaction occurring in solution during which the atmospheric pressure remains constant

Constant-pressure Calorimeter

4. Differential scanning calorimeter

In a differential scanning calorimeter (DSC), heat flow into a sample usually contained n the small aluminium capsule or 'pan' is measure differentially. By comparing it into an empty reference pan.

Differential-scanning Calorimeter

5. Isothermal titration calorimeter

In an isothermal titration calorimeter, the heat of reaction is used to follow a titration experiment

.

Isothermal-titration Calorimeter

.:The Introduction to Calorimeter:.

A calorimeter is a device for calorimetry, the science of measuring the heat of chemical reaction or physical changes as well as heat capacity. The word calorimeter is derived from the Latin word 'calore', meaning heat. Differential scanning calorimeters, isothermal calorimeters, titration calorimeters and accelerated rate calorimeters are among the most common types. A simple calorimeter just consists of a thermometer attached to a metal container full of water suspended above a combustion chamber.

To find the enthalpy change per mole of a substance A in a reaction between two substances: A and B, the substances are added to a calorimeter and the initial and final temperatures (before the reaction started and after it has finished) are noted. Multiplying the temperature change by mass and specific heat capacities of the substances gives a value for the energy given off or absorbed during the reaction. Dividing the energy change by how many moles of A were gives its enthalpy change of reaction. This method is used primarily in academic teaching as it describes the theory of calorimetry. It does not account for the heat loss through the container or the heat capacity of the thermometer and container itself. In addition, the object placed inside the calorimeter show that the object transferred their heat to the calorimeter and into the liquid, and the heat absorbed by the calorimeter and the liquid is equal to the heat given off by the metal.

Figure: Bomb Calorimeter

The Introduction to Thermochemistry

Thermo chemistry is the study of the energy and associated with chemical reaction and/or physical transformation. A reaction may release or absorb energy, and a phase change may do the same, such as in melting and boiling. Thermo chemistry focuses on these energy change, particularly on the system's energy exchange with its surroundings. Thermo chemistry is useful in predicting reactant and product quantities throughout the course of a given reaction. It is also used to predict whether a reaction is spontaneous or non-spontaneous, favourable or unfavourable. Endothermic reactions absorb heat. Exothermic reactions release heat. Thermo chemistry coalesces the concepts of thermodynamics with the concept of energy in the form of chemical bonds. The subject commonly includes calculations of such quantities as heat capacity, heat of combustion, heat of formation, enthalpy, entropy, free energy, and calories.