The properties of water which gives the definition of the origin of the calorie is the amount of temperature change experienced by water or release time to take some heat. The general term for these properties is called the heat capacity is defined as the amount of heat required to change the temperature of an object by 1 0 C.
Heat capacity is extensive, which means that the amount depending on the sample size. For example to raise the temperature of 1 g of water by 1 0 C required 4.18 J (1 cal), but to raise the temperature of 100 g of water by 1 0 C takes 100 times more energy is 418 J. So that 1 g of the sample had a heat capacity of 4.18 J / 0 C while 100 g samples of 418J / 0 C.
Intensive nature of the heat capacity is related to the type of heat (specific heat) which is defined as the amount of heat required to raise the temperature of 1 g of substance by 1 0 C. For water, its specific heat is 4.18 JG-1C-1. Most substances have a smaller specific heat than water. For example iron, only the specific heat 0.452 J g -1 0 C -1. Means less heat is needed to heat 1 g of iron by 1 0 C than water or can also mean that the amount of heat that will raise the temperature of 1 g of iron is greater than on raising the temperature of 1 g of water.
The amount of the specific heat for water due to a little influence from the sea to the weather. In winter the sea water to cool slower than the mainland so that air moves from sea to land is hotter than the air from land to sea. Likewise in the summer, the sea water is slower to heat than the mainland.
The formula:
q = m.c. Δ't
Description:
q = amount of heat (Joule)
m = mass of substance (g)
Δt = change in temperature t final - t initial)
c = heat typeCalorimetry
Calorimetry calorimetry
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Enthalpy changes
Enthalpy = H = Heat of reaction at constant pressure = Qp
Enthalpy change is the change in energy that accompanies the event of chemical changes at a constant pressure.
a.
Termination of bonds requires energy (= endothermic)
Example: H 2 → 2H - a kJ; DH = + akJ
b.
Bond formation to give the energy (= exothermic)
Example: 2H → H 2 + a kJ; DH =-a kJ
Term used in the enthalpy change:
1.
Standard enthalpy Pembentakan (DHF):
DH animal lays forming 1 mole of compound directly from its elements are measured at 298 K and a pressure of 1 atm. Example: H 2 (g) + 1 / 2 O 2 (g) → H 2 0 (l); DHF = -285.85 kJ
2.
Enthalpy of decomposition:
DH from the decomposition of 1 mol of the compound directly into its elements (= opposite of DH formation). Example: H 2 O (l) → H 2 (g) + 1 / 2 O 2 (g) DH = +285.85 kJ
3.
Standard Enthalpy of Combustion (DHC):
DH to burn 1 mole of compounds with O 2 from the air measured at 298 K and a pressure of 1 atm. Example: CH 4 (g) + 2o 2 (g) → CO 2 (g) + 2H 2 O (l); DHC = -802 kJ
4.
Reaction enthalpy:
DH equation of a reaction in which substances contained in the equation is expressed in units of moles and the coefficients of the equation is simple round. Example: 2Al + 3H 2 SO 4 → Al 2 (SO 4) 3 + 3H 2; DH = -1468 kJ
5.
Enthalpy of Neutralization:
DH produced (always exothermic) in the reaction of neutralization of acid or base. Example: NaOH (aq) + HCl (aq) → NaCl (aq) + H 2 O (l) DH = -890.4 kJ / mol
6.
Lavoisier-Laplace law
"The amount of heat that is released to the formation of 1 mole of substance from the elements-unsurya = amount of heat required to decompose the substance into its constituent elements."
Meaning: If the reaction is reversed then the sign of heat that is formed is also reversed from positive to negative or vice versa Example:
N 2 (g) + 3H 2 (g) → 2NH 3 (g) DH = - 112 kJ
2NH 3 (g) → N 2 (g) + 3H 2 (g) DH = + 112 kJEnthalpy of formation, combustion and decomposition
Thermochemical data are generally set at a temperature of 25 0 C and a pressure of 1 atm, hereinafter referred to standard conditions. Enthalpy changes are measured at a temperature of 25 0 C and a pressure of 1 atm is called the standard enthalpy change and is expressed with the symbol Δ H 0 or ΔH298. While the changes in enthalpy measurement does not refer to the conditions of measurement represented by the symbol ΔH alone.
Is the molar enthalpy of the reaction enthalpy change associated with the quantity of substance involved in the reaction. In the known thermochemical various molar enthalpy, such as the enthalpy of formation, decomposition enthalpy, and enthalpy of combustion.The formation enthalpy
There is a range of important thermochemical equation associated with the formation of one mole of a compound of unsurunsurnya. Enthalpy changes associated with this reaction is called the heat of formation or enthalpy of formation is given the symbol ΔH f. For example thermochemical equation for the formation of water and steam at 100 0 C and 1 atm respectively.
RM1
How can we use this equation to obtain the heat of vaporization of water? Clearly equation (1) should be behind us, and then summed with equation (2). Do not forget to change the sign of ΔH. (If the formation of H 2 O (l) exothermic, as reflected by a negative ΔH f, the reverse process must be endothermic) which means a positive exothermic which means to be endothermic.Exothermic
Exothermic (heat producing) exothermic (heat producing)
RM2Endothermic
rm311
When we add the equation (1) and (2), we can
rm410
And heat the reaction =
rm56
Note that the heat of reaction for all the changes together with the heat of formation of reaction products minus the heat of formation of reactants. Generally it can be written:
rm65
Price changes in reaction enthalpy can be influenced by the temperature and pressure conditions during the measurement. Therefore, the necessary conditions of temperature and pressure are to be given to any thermochemical data.Enthalpy of Combustion
The reaction of a substance with oxygen is called combustion reactions. Flammable substances that are the elements carbon, hydrogen, sulfur, and various compounds of these elements. Said to be perfect if the combustion of carbon (c) burned into CO2, hydrogen (H) burned into H2O, sulfur (S) burned to SO2.
Enthalpy changes in the complete combustion of 1 mol of a substance measured at 298 K, 1 atm is called the standard enthalpy of combustion (standard enthalpy of combustion), which is expressed by Δ Hc 0. Enthalpy of combustion is also expressed in kJ mol -1.
Price enthalpy of combustion of various substances at 298 K, 1 atm are given in Table 3 below.
Table 3. Enthalpy of combustion of various substances at 298 K, 1 atm
gb18
The burning of gasoline is an exothermic process. If gasoline is considered consisting of isooktana, C8H18 (one component of gasoline) determine the amount of heat released on combustion of 1 liter of gasoline. Known enthalpy of combustion isooktana = -5460 kJ mol -1 and a density of isooktan = 0.7 kg L -1 (H = 1; C = 12).
Answer:
Isooktana enthalpy of combustion is - 5460 kJ mol -1. Mass of 1 liter of gasoline = 1 x 0.7 kg liter L-1 = 0.7 kg = 700 grams. Mol gram/114 isooktana = 700 grams = 6.14 mol mol -1. So the heat released on combustion of 1 liter of gasoline is: 6.14 x 5460 kJ mol -1 = 33524.4 kJ mol.Perfect combustion and Not Perfect
Fuel combustion in vehicle engines or in the industry do not burn completely. Complete combustion of hydro carbon compounds (fossil fuels) to form carbon dioxide and water vapor. While imperfect combustion to form carbon monoxide and water vapor. For example:
a. Complete combustion isooktana:
C8H18 (l) +12 ½ O2 (g) -> 8 CO2 (g) + 9 H2O (g) ΔH = -5460 kJ
b. Imperfect combustion isooktana:
C8H18 (l) + 8 ½ O2 (g) -> 8 CO (g) + 9 H2O (g) ΔH = -2924.4 kJ
Arson not Perfect Impact
As shown in the example above, imperfect combustion produces less heat. Thus, imperfect combustion reduces fuel efficiency. Another disadvantage of incomplete combustion of carbon monoxide gas is produced (CO), which are toxic. Therefore, imperfect combustion will pollute the air.The decomposition enthalpy
Decomposition reaction is the reverse of reaction formation. Therefore, in accordance with the principle of conservation of energy, equal to the value of the enthalpy of the decomposition enthalpy of formation, but the opposite sign.
Example:
Known Δ Hf 0 H2O (l) = -286 kJ mol -1, the enthalpy of the decomposition of H2O (l) into hydrogen gas and oxygen gas is + 286 kJ mol -1
H2O (l) -> H2 (g) + ½ O2 (g) ΔH = + 286 kJ
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Reaction heat and thermochemical
Relations system with the environment Relations with environmental systems
The study of heat is called a thermochemical reaction that is part of the branch of a larger science of thermodynamics. Before talking about the principle of this thermochemical we proceed, will be made once the definition of some terms. One of the terms that will be used is the system. The system is part of the universe that we are studying. It may be for example a chemical reaction that occurs in a beaker. Outside the system is the environment. In explaining a system, we must analyze its properties appropriately. Given temperature, pressure, number of moles of each substance and a liquid, solid or gas. After all these variables are determined means that all the properties of the system is certain, we have described the state of the system.
When changes occur in a system it is said that the system moves from one state to another state. When the system is isolated from the environment so that no heat can flow then changes that occur in the system is adiabatic change. During the adiabatic change, the temperature of the system will shift, when the exothermic reaction will go up while going down when the endothermic reaction. When the system was isolated from its environment, then the heat will flow between the two, so if there is a reaction, the temperature of the system can be made permanent. Changes that occur at constant temperature is called the change isotermik. It has been said, if the reaction is exothermic or endothermic then on the chemicals involved will be a change of potential energy. We measure the heat of reaction will be equal to the change of this potential energy. From now on we will use this change in some quantity that need to be enforced some rules to declare changes in general.
The symbol Δ (Greek letter for delta) is generally used to indicate a change in quantity. For example changes in temperature can be written by ΔT, where T represents temperature. In practice, usually in the show change is by reducing the final temperature with the temperature at first.
ΔT = T final - T initial
Likewise, changes in potential energy
(Ep) Δ (E.P) = EP late - early EP
From this definition obtained an agreement in algebraic sign for exothermic and endothermic changes. In the exothermic change, the potential energy of the reaction is lower than the potential energy EP reagents means lower end of the first EP. So the price ÷ EP has a negative price. Opposite to the endothermic reaction, where the price ÷ EP is positive.Exothermic and endothermic reactions
Endothermic event (right) and exothermic (left) endothermic event (right) and exothermic (left)Exothermic reaction
Exothermic reaction occurs at the heat transfer from the system into the environment or on the reaction heat is released. In the exothermic reaction ΔH = negative prices (-)
Example:
C (s) + O 2 (g) → CO 2 (g) + 393.5 kJ;
ΔH = -393.5 kJEndothermic reaction
In reaction to the heat transfer occurs from the environment to the system or to the reaction heat is needed. At the price endothermic reaction ΔH = positive (+)
Example:
CaCO 3 (s) → CaO (s) + CO 2 (g) - 178.5 kJ; ΔH = +178.5 kJ
The process of exothermic and endothermic processes The process of exothermic and endothermic process
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Definition of thermochemical
thermochemical thermochemical can be defined as part of chemistry that studies the dynamics of chemical reactions or changes by observing thermal / thermal only. One of applied science in everyday life is a chemical reaction in our bodies where the production of energy-the energy required or issued for all the tasks that we do. Combustion of fuels like oil and coal used for electricity generation. Gasoline burned in a car engine will produce power that causes the car running. If we have a gas stove means we burn methane (the main component of natural gas) that produce heat for m gold ak. And through a sequence of reactions called metabolism, food you eat will produce the energy we need for the body to function.
Almost all chemical reactions there is always the energy is taken or removed. Let us examine the occurrence of this and how do we know of any changes in energy.
Thermochemical thermochemical events Events
Suppose we will perform a chemical reaction in an enclosed area so that no heat can escape or enter into the reaction mixture. Or the reaction is carried out in such a way that the total energy remains the same. Also suppose that the potential energy of the reaction is lower than the potential energy of reagents so that reactions occur when there is a decrease of potential energy. But this energy can not just disappear because the total energy (kinetic and potential) should remain constant. Therefore, when its potential energy falls, then the mean kinetic energy must increase the potential energy turns into kinetic energy. The addition amount of kinetic energy will cause the price of the average kinetic energy of molekulmolekul ride, which we see as a rise in temperature of the reaction mixture. The reaction mixture became hot.
Most chemical reactions are not sealed from the outside world. When the reaction mixture to heat as described below, the heat can flow around. Any changes that can release energy to the surroundings are called exothermic changes. Note that if there is an exothermic reaction, the temperature of the reaction mixture will rise and the potential energy of chemical substances in question will come down.
Sometimes chemical changes occur when there is increased potential energy of the substances concerned. When this happens, then the kinetic energy would go down so that its temperature is also down. When the system is not closed in around him, the heat can flow into the reaction mixture and the change is called endothermic change. Note that if there is an endothermic reaction, the temperature of the reaction mixture will decrease and the potential energy of the substances involved in the reaction will go up.
Event of a fire producing heat the fire produces heat eventsMeasurement of Energy in Chemical Reactions
Standard international unit for energy is Joule (J) derived from the kinetic energy. One joule = 1 kgm 2 / s 2. Equivalent to the amount of energy that belongs to an object with a mass of 2 kg and a speed of 1 m / sec (if in units of English, the object with a mass of 4.4 lb and the speed of 197 ft / min or 2.2 mile / hour).
1 J = 1 kg m 2 / s 2
Smaller unit of energy used in physics called the ERG that cost = 1 × 10 -7 J. In referring to the energy involved in the reaction between the reactant molecule size is usually replaced with larger units of kilojoules (kJ). One kilojoules = 1000 joules (1 kJ = 1000J).
All forms of energy can be converted entirely into heat and when a chemist measures the energy, usually in the form of heat. The usual way is used to express heat is called calorie (cal abbreviation). The definition is derived from the effect of heat on the temperature of the object. At first calorie is defined as the amount of heat required to raise the temperature of 1 gram of water with temperatures from 15 0 C for 1 0 C. Kilocalories (kcal) as well as kilojoules are units that are better suited to express the energy changes in chemical reactions. The unit is also used to indicate kilocalories of energy contained in food.
Upon the acceptance of the SI, is now also joules (or kilojoules) and calories preferably redefined in SI units. Now calories and kilocalories are defined exactly as follows:
1 cal = 4.184 J
1 kcal = 4.184 kJquestion :
1. What conditions ideal calorimeter?
What type of petroleum based differences in boiling point and how the mechanism of manufacture synthetic petroleum using marine algae?
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