VIDEO : THERMOCHEMICAL

THERMOCHEMICAL

In the Thermochemical there is The law of conservation of energy  energy can not be created or destroyed, can only be changed from one form to another. 

Exoterm Reactions And Endoterm

Basically, enthalpy changes occur because of the energy transfer between the system and the  environment. The system is something that becomes the center of attention and observation in a reaction, while the environment is everything that is outside a system .

1.      Exothermic reaction

Exothermic reaction is a reaction that occurs with the release of heat from the system to the environment or heat-releasing reactions. One feature of exothermic reactions is that during the  reaction process, the system temperature rises. Burn books are examples of exothermic reactions.

Example Exothermic reaction :

1. Burning Reaction

2. Respiratory Reactions

3. Formal Reactions

4. Water Becomes Ice

5. Water Vapor Becomes Water 

2.      Endothermic reaction

The endothermic reaction is a reaction accompanied by heat transfer from the environment to the system, or briefly it can be said that the endothermic reaction is a reaction that the system absorbs heat. One characteristic of the endothermic reaction is that during the reaction there is a decrease in temperature so that to return to its initial temperature state, the system must absorb the heat.

Example Endothermic reaction :

1. Ice Becomes Water

2. Water Become Water Vapor

3. Photosynthesis Reactions

Thermochemical Equations

The equation of the reaction which involves the change in its intercept is called the thermochemical equation. The ΔH value written in the thermochemical equation is adjusted to the stoichiometry of the reaction. This means that the number of moles of substances involved in the reaction is equal to the reaction coefficient.

Since the enthalpy of the reaction is also dependent on the form of the substance to be expressed, ie by applying the s index to the solid, l for the liquid, and g to the gaseous agent. Consider the following example.

Example: In the formation of 1a mol of water from hydrogen gas with oxygen gas released 286 kJ. The word "released" states that the reaction is classified as exothermic. H = -286 kJ For each mole of water formed. The thermochemical equation is:

H2 (g) + 1/2 O2 (g) -> H2O (l) ΔH = -286 kJ

Or

2 H2 (g) + O2 (g) -> 2 H2O (l) ΔH = -572 kJ

(Since the reaction coefficient is multiplied by two, then the price of ΔH must also be multiplied by two).

Pricing Of Enthalpy Changes With Calorimeter

Formula :

Q= m.c. DT

Q= heat absorbe

M= mass

C= heat type of solution

DT = temperature change 

Example :

In the calorimeter there is a substance the reacts exothermically and it turn out that 0.5 kg of water that surrounds it as a solvent has a increase in temperature of 3c and calor water type 4,2. what is the caloric reaction of the substance released by the reaction ?

Answer:

m    = 0.5 kg = 500 gram

DT  = 3^oC = 273 + 3 = 276^oK

c     = 4,2 J/gram ^oK   

Q    = m.c. DT

       = 500 ´ 4,2 ´ 276

       = 579.600 Joule

       = 576,6 KJ

Watching this video in link :

https://youtu.be/7JvJdLhV4D8