Questions

A chemical reaction in which involves the absorption of heat from the environment is called a Endothermic reaction. 

Examples : Dissolving ammonium chloride in water, photosynthesis, melting ice cubes, mixing of potassium chloride with water,...

In the contrast, chemical reactions involving release of heat are known as exothermic reactions.

Examples : Combustion, coal is burnt, mix of CaO with water,...

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Holland is also known as Netherlands, which means "Low lands". Dutch Engineers reclaimed considerable part of the seabed by building dykes and pumping out the sea water into canals. Some houses in Holland are below sea level. Belgium has also Low lands  bordering the North Sea and dykes are constructed to control the encroachment of the sea.

Covalent bonding occurs when pairs of electrons are shared by atoms. Atoms will covalently bond with other atoms in order to gain more stability, which is gained by forming a full electron shell. By sharing their outer most (valence) electrons, atoms can fill up their outer electron shell and gain stability.

Examples of compounds with covalent bonds ::

HCl, CO2, O2,... 

Supply curves tend to be more elastic in the long run, because there is time for firms to enter or leave the industry.

By whom was the food burned?