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.

Salt	А,g.	Т1	В,g.	Т2
CaCl2	126,9	23,2	42,2	-55
CH3COONa	51,1	15,4	-	-
FeCl3	-	-	49,7	-55
KCl	30	12,6	30	-11,1
KNO3	-	-	13	-2,9
K2SO4	-	-	13	-2,9
MgCl2	-	-	27,5	-33,6
MgSO4	41,5	8,0	23,4	-3,9
NaCl	36	2,5	30,4	-21,2
Na2CO3	14,8	9,1	6,3	-2,1
NaNO3	75	18,5	59	-18,5
Na2S2O3	70	18,7	42,8	-11
NH4Cl	30	18,4	25	-15,8
NH4NO3	60	27,2	45	-17,3
(NH4)2SO4	75	6,4	62	-19

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
Al2O3	+1676	H2O	+286
CO	+110	CO2	+394
CS2	-88,7	CaO	+635
CaCO3	+1207	CaSiO3	+1635
Ca3(PO4)2	+4121	Fe2O3	+822
MgO	+602	MgSiO3	+1549
NO	-90,3	NO2	-33,2
NH3	+45,9	SiO2	+911