Use the following equations to answer the next five questions:
i. h2o --> h2o
ii. na+ + cl- ag+ + no3- --> agcl + na+ + no3-
iii. ch3oh + o2 --> co2 + h2o
iv. 2h2o --> 2h2 + o2
v. h+ + oh- --> h2o
(a) which equations describes a physical change?
(b) which equation identifies the reactants and products of a combustion reaction?
(c) which equation is not balanced?
(d) which is a net ionic equation?

(a) i

(b) iii

(c) iii

(d) v

Explanation:

(a) A physical change does not alter the identity of the substance. Here the water remains water, but may change undergo a physical change such as vaporization or freezing.

(b) A combustion reaction usually involves the exothermic reaction of oxygen with another molecule to form carbon dioxide and water

(c) The reaction may be balanced as follows: CH₃OH + 3/2O₂ ⇒ CO₂ + 2H₂O

(d) A net ionic equation only takes into account the species that underwent a chemical change. Equation ii. for example, is not a net ionic equation because the Na⁺ and NO₃⁻ did not change in any way.

why is arctic sea ice important? arctic sea ice keeps the polar regions cool and moderate global climate. sea ice has a bright surface; 80 percent of the sunlight that strikes it is reflected back into space. as sea ice melts in the summer, it exposes the dark ocean surface.

1. for the first question, we must find the mass of the anhydrous salt, mgso₄. the molar mass for mgso₄·7h₂o is 246.47 g/mol, while that of mgso₄ is 120.37 g/mol.7.834 g mgso₄·7h₂o * 1 mol mgso₄·7h₂o/246.47 g * 1 mol mgso₄/1 mol mgso₄·7h₂o * 20.37 g mgso₄/mol = 0.647 g mgso₄

2. mass of water = mass of sample - mass of anhydrous salemass of water = 7.834 - 0.647 = 7.19 gpercent water in hydrate = 7.19/7.834 * 100 = 91.74%