C. Tetraphosphorus trisulfide
Answer:
-1071 Joules
Explanation:
The Joule was introduced as the SI unit for energy in 1925. One calorie is equal to approximately 4.184 joules(J). This is a conversion factor that we can write two ways:
(1cal/4.184J) or (4.184J/1cal)
(265 cal)*(4.184J/1cal) = 1071 J
Since the energy is leaving the system, it should be written with a minus sign: -1071J
Answer:
4.525% is the percentage by volume of oxygen in the gas mixture.
Explanation:
Total pressure of the mixture = p = 4.42 atm
Partial pressure of the oxygen = 
Partial pressure of the helium = 
(Dalton law of partial pressure)





According Avogadro law:
(At temperature and pressure)
Volume occupied by oxygen gas =
Total moles of gases = n = 1 mol
Total Volume of the gases = V


Percent by volume of oxygen in the gas mixture:

Answer:
C) Covalent bonds come about because of a sharing of electrons; ionic bonds do not.
Explanation:
There are two main types of chemical bonds- covalent and ionic/electrovalent bonds.
Ionic bond: Ionic or electrovalent bonds are characterized by the transfer of electrons from electropositive atoms (metals) to electronegative atoms (non-metals). The metal atoms after donating their electrons become positively charged ions (cations) while the non-metal atoms after accepting electrons become negatively charged ions (anions). Strong electrostatic forces of attraction constitutes ionic bonds.
Covalent bond: Covalent bonds are formed by the sharing of electrons by the atoms involved in the bond; usually between atoms of comparable electronegativities or atoms of the same element. The shared electrons are contributed by each of the atoms involved in the bonding or may be contributed by only one of the atoms. In covalent bonding, molecules rather than ions are formed.
Answer is B.
As the diaphragm contracts and flattens, it increases the volume of the thorax where the lungs are located. This results in a decrease in pressure (Boyle’s Law, if you know it) that creates a pressure gradient from outside to inside. This is what causes air to move into the lungs.