Specific Heat is:
-the amount of energy required to raise the temperature of 1g of a substance 1°C
-specific heat is symbolised as Cp or C
-has units of J/g °C
-J stands for Joules, which is a unit of energy
Most often used in equation: q = mΔTCp
q = energy in J
m = mass in g
ΔT = change in temperature
Cp = specific heat
ExampleHow much energy is required to raise the temperature of 345.34g of Aluminium from 35.0°C to 250.00°C ? The specific heat of Aluminium is .90 J/Cpq = mΔTCp
q = 345.34g(250.00°C - 35.0°C)0.09J/g°C
from there its just simple Algebra.
q = 66,823.29J
However, not all problems will be as simple as the one above. Some may require up to 3+ equations that can include Enthalpy or ΔH which leads to using a Change of State Graph.
(Enthalpy is the heat content of a system at constant pressure).
(A thermochemical equation is a chemical equation that includes enthalpy change).
The change in enthalpy is represented in equations as delta H.
Make sure that the thermochemical equation is balanced. Then determine whether this is an endothermic or exothermic. ( if the delta H value given is positive, then the reaction is endothermic. if it is negative, then it is exothermic). If the reaction is endothermic, then add the delta H value to the reactants (right side of the equation) in kJ. If it is exothermic, add it to the products (left side) in kJ.
****If needed use Hess' Law
1. if reverse equation, then change the sign on the delta H value
2. if multiply/divide the equation, then do the same to the delta H value
3. add equations and add delta H values
Draw a born-haber cycle.
Remember that the sum of the reactions enthalpy change is all of the individual changes added together.
You could use Hess' law to draw one of his triangle things, but i find that difficult.
Enthalpy of a chemical species is expressed in joules/mol. No temperature unit is included in enthalpy and thus temperature does not play a role in its calculation.
change in enthalpy = enthalpy of reactants - enthalpy of products
enthalpy values of chemical species can be found in a merck index
There are many possible types of chemistry problems; it is not possible to give a generic answer for all of them.
The temperature change is needed to calculate the enthalpy change.
Changing the temperature
the atoms (or molecules) within the substance move slower, as temperature decreases.
the standard enthalpy change of vaporization DHov is the enthalpy change when one mole of a substance is transformed into a gas enthalpy change is the term we use to describe the energy exchange that occurs with the surroundings at a constant temperature and pressure so to work it out, use the formula DH = cmDT DH - the enthalpy change c - the specific heat capacity of butanol (kJ kg-1 °C-1) m - the mass of butanol heated (kg) DT - the change in temperature of the butanol (°C) so there is no general enthalpy change of butanol, it depends on the factors above. the specific heat capacity of butanol, the mass of butanol heated, and the change in temperature of the butanol should be given to you in order to work the enthalpy change of vaporization of butanol if there is a rise in temperature, the reaction is exothermic and if there is a drop in temperature the reaction is endothermic. exothermic reactions have a negative enthalpy change, and therefore endothermic reactions have a positive enthalpy change. hope it helped (:
Enthalpy is the measurement of total energy change of a reaction. The energy of bond formation and bond breaking can be used to calculate the bond enthalpy of the reaction. Bond enthalpy is the enthalphy change when 1 mol of bond is broken. Therefore the general equation to calculate the enthalpy change is energy of bond broken subtract by energy of bond formation.
Enthalpy is a particular amount of heat that is produced or released at a given pressure. There are specific equations that must be used to calculate enthalpy.
The temperature change is needed to calculate the enthalpy change.
Wetblb= -0.015991*enthalpy*enthaply+2.374*enthaply+7.5089
Changing the temperature
Generally enthalpy is analgous to the energy of a material at a particular temperature and pressure. It is calculated to determine the energy a material holds, or more often, enthalpy differences are calculated to determine how much energy is required to bring a material from one temperature and pressure to another temperature and pressure.
the atoms (or molecules) within the substance move slower, as temperature decreases.
Assuming chemical energy means the enthalpy change (measured in joules), there are several methods to calculate chemical energy, although there is no one 'formula'. The simplest way is to calculate the bond energies between the atoms in the molecules and subract the total initial energy from the total final energy. If bond energies aren't provided, more complex methods are required. If you're looking for the change in enthalpy in the reaction A --> D, and are given the changes in enthalpy for A --> B, B --> C, and C --> D, then adding the enthalpy changes for the given reactions will give you the desired enthalpy change.
Enthalpy is the amount of energy in a system and when this changes (when a reaction happens), the energy is either released (exothermic) or absorbed (endothermic) and this energy is usually released or absorbed as heat. Therefore when the enthalpy decreases, heat is released from the system making it exothermic. In contrast, when the enthalpy increases, heat is absorbed making it endothermic.
the standard enthalpy change of vaporization DHov is the enthalpy change when one mole of a substance is transformed into a gas enthalpy change is the term we use to describe the energy exchange that occurs with the surroundings at a constant temperature and pressure so to work it out, use the formula DH = cmDT DH - the enthalpy change c - the specific heat capacity of butanol (kJ kg-1 °C-1) m - the mass of butanol heated (kg) DT - the change in temperature of the butanol (°C) so there is no general enthalpy change of butanol, it depends on the factors above. the specific heat capacity of butanol, the mass of butanol heated, and the change in temperature of the butanol should be given to you in order to work the enthalpy change of vaporization of butanol if there is a rise in temperature, the reaction is exothermic and if there is a drop in temperature the reaction is endothermic. exothermic reactions have a negative enthalpy change, and therefore endothermic reactions have a positive enthalpy change. hope it helped (:
enthalpy of air leaving the compressor minus enthalpy of air entering the compressor
q( enthalpy of heat in Joules-energy ) = Mass of steel * heat capacity of steel * ( Temperature final - temperature initial )
Enthalpy is the measurement of total energy change of a reaction. The energy of bond formation and bond breaking can be used to calculate the bond enthalpy of the reaction. Bond enthalpy is the enthalphy change when 1 mol of bond is broken. Therefore the general equation to calculate the enthalpy change is energy of bond broken subtract by energy of bond formation.