Chemists use reactions to generate a desired product. For the most part, a reaction is only useful if it occurs at a reasonable rate. For example, a reaction that took 8,000 years to complete would not be a desirable way to produce brake fluid. However, a reaction that proceeded so quickly that it caused an explosion would also not be useful (unless the explosion was the desired result). For these reasons, chemists wish to be able to control reaction rates. In order to gain this control, we must first know what factors affect the rate of a reaction. We will discuss some of these factors in this section.
The solution contains 39.4% of LiF. Assume that the solution is 100ml. The molar mass of LiF is 25.939, the amount of LiF in mole would be: 100ml * 1g/ml * 39.4%/ 25.939g/mol= 1.52 mol LiF
Then the mass of the water would be: 100gram- 39.4g= 60.6g
If the molar mass of water is 18.015 the mole of the water would be: 60.6g/ 18.015g/mol= 3.36 mol
.
The mole fraction would be:1.52 mol/ 1.52+3.36= 0.339
Answer:
Explanation:
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In this case, according to the given information, it turns out possible for us to solve this problem by using the following equation, defined in terms of energy, Planck's constant, wavelength and speed of light:
Thus, we solve for the wavelength as shown below:
And finally plug in the energy, Planck's constant and speed of light to obtain:
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Answer: an ice pack getting cold (due to ammonium nitrate dissolving in water inside the pack)
Explanation:
Endothermic reactions: These are the reactions in which energy is required in the reaction. The energy of the products are more than the energy of the reactants.
Exothermic reactions: These are the reactions in which energy is released in the reaction. The energy of the products is less than the energy of the reactants.
a) water droplets condensing on a soda can on a hot summer day : As the gaseous molecules are changing into liquid phase, energy is released and is exothermic
b) an ice pack getting cold (due to ammonium nitrate dissolving in water inside the pack) : As the temperature is decreasing , energy is absorbed by the surroundings and thus is endothermic
c) thermite reaction between iron(III) oxide and aluminium (spectacular flames are observed) : As flames are produced, the energy is released and thus is exothermic
d) freezing water to make ice cubes : As the liquid molecules are changing into solid phase, energy is released and is exothermic
Alkali metals
Hydrogen only needs one more valence electron to fill it's out shell. So it belongs with the alkali metals.
