Getting low temperature can be achieved even at home, preparing cooling mixture.
Cooling mixture- this is mixtures, which consist of chemicals, when mixed the temperature of the mixture is lowering. To prepare the cooling mixture, usually using salt solution in water or salt solution and snow. In the language of chemistry is endothermic, i.e. the reaction with the absorption of ambient heat.
Let us consider cooling mixture.
To obtain a low temperature, often use a mixture of salt and water or snow. So, when mixing А parts of salt and 100 ml of water will lowering the temperature on T1, if takes В of salt and snowore ice, the temperature decreases to Т2.
There is exothermic reaction, is a chemical reaction in which heat and energy is released (for example, combustion is a chemical reaction accession oxygen)
There are chemical laws, which allow to calculate the heat effect of reactions. In the calculations it is necessary to consider, all thermochemical reactions occur to standard conditions (i.e. 25 0degrees of Celsius and 10 5 PA taking into account the concentration of 1 mol/liter of solution).
If in the process of chemical reaction heat is liberated, then put a "+"sign, if absorbed, the sign "-". For example
C + S →CS2 - 88,7 kJ
the carbon interacts with sulfur to form sulfides of carbon, when it is absorbed to 88.7 kJ of heat. Below is a table showing the quantity of heat of formation of some substances
|Substance||Heat, kJ/mol||Substance||Heat, kJ/mol|