Why is water a liquid at stp while carbon dioxide is a gas?

Answer 1

Carbon dioxide is a gas at room temperature because its molecules have enough thermal energy at room temperature so that they won't stick closely together. Heat (or lack of it) is what drives change of state.

Silicon dioxide is sand.

More Information:

Theoretically SiO2 might be expected to look like CO2: ::O = C = O::

However, since the Si-atom is much bigger than C, it is not energetically favorable to the formation of double bonds with the smaller oxygen atoms. The delocalized electrons (in the perpendicular p-orbitals) are too far away from the oxygen atoms to prefer this stretched state.

Instead, SiO2 is the basic formula unit of a tetrahedral tertiary structure. Each Si-atom covalently binds four oxygen atoms with a single bond. A more accurate formula would be SiO4/2. Each oxygen binds two Si-atoms, so that a crystal structure is formed. This network is very strong resulting in a melting point that is way higher than CO2.

Carbon and Oxygen form discrete molecules, with two oxygen atoms to every carbon atom, which can remain independent as gas molecules. Silicon however, doesn't form discrete molecules but rather, makes a long chain, crystalline form in roughly a tetrahedral arrangement. Solid Silicon dioxide is therefore, one great big molecule and melting it requires the breakage of a large number of covalent bonds, which requires a lot of energy. Vaporizing it, to form a gas, would require even more energy.

This is why SiO2(/4) is solid sand while CO2 is a gas, and difficult to solidify.

Answer 2

Although carbon dioxide has a greater molecular mass than water, water is a liquid at room temperature while carbon dioxide is a gas because of the strong intermolecular forces that hold water molecules together. Primarily, it is water's hydrogen bonds that keep it liquid at room temperature.

Answer 3

In water the oxygen pulls electrons away from the hydrogen. Because the molecule has a bent shape this creates a partial positive charge at one end and a partial negative charge at the other. This is called a polar molecule. The positive end of on molecule attracts the negative end of another, much like the poles of a magnet. Because of this the molecules tend to stick together, forming a liquid.

The oxygen also pulls electrons away from the carbon in carbon dioxide, but CO2 is a linear molecule. The result is that the oxygen atoms have an equal pull on the electrons in opposite directions, and so cancel each other out. Because of this carbon dioxide molecules are nonpolar and less strongly attracted to each other.

Answer 4

Water is a liquid at STP (standard temperature and pressure) because its intermolecular forces are stronger, allowing water molecules to stay close together. Carbon dioxide, on the other hand, is a gas at STP because its intermolecular forces are weaker, causing its molecules to spread out and move freely.