Chemistry, 03.02.2020 14:50 LilXan420

Which describes a solution that contains a system at equilibrium?

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The solution where the color is not changing is at eqiulibrium. If the color is still changing, then the concentrations in the solution are still changing and the system is not at equilibrium.

2.
When Br- is added, the reaction occurs in the forward direction to use up some of the excess Br- added (LeChatelier's principle).
a.
Cu(H2O)6+2 - decreases
Br- - increases, because not all the added Br- is consumed
H2O - increases
CuBr4-2 - increases
b.
K doesn't change unless the temperature changes.
c.
The color would change from bluish to greenish because te Cu(H2O)2+ (blue) is decreasing and the CuBr4(2-) (green) is increasing.
d.
The tube would feel cooler because the forward reaction occurs to use up some of the added Br-. Heat is removed from the surroundings when the forward reaction occurs, so the tube feels cooler.
3.
Mg(OH)2(s) <==> Mg+2 + 2 OH- To make this reaction proceed to the right, you need to remove either Mg2+ or OH-. One way of removing OH- is to add an acid. The molecular equation is: Mg(OH)2 + 2HCl ---> MgCl2 + 2H2O The HCl effectively removes OH-, which causes the Mg(OH)2 to dissolve to replace some of the OH- being removed by the acid.
4.
CO + 2H2 <==> CH3OH + heat
Both a. and c.
Adding CO causes the forward reaction to occur as the system tries to use up some of the excess CO.
Removing CH3OH also causes the forward reaction to occur as the system tries to replace some of the CH3OH being removed.

Answer from: Quest

pre-sliced bread is a relatively recent development in baking technology. previous to that, it was always sold in a bakery in daily-made contiguous loaves with no wrapping, and was moderately perishable, usually being used with a day or two (which is why every bakery had a discounted “day-old” bread table.) therefore, pre-sliced bread would grow stale quickly. the hard crust provided a protective layer, and once the exposed dry slice left from the previous cut was removed, the interior was still soft.

what keeps bread soft is the moisture retained in the crumb (the light spongy part that’s not crust). the reason the crust develops is the surface of the dough gets exposed to hot dry air during baking which browns the outer layer and seals it, preventing all the moisture from escaping the dough. longer exposure to air will also eventually cause your bread to lose flavor and become stale.

people were used to cutting slices as they needed them and storing bread in a specially-made wooden or metal breadbox or pail with a lid to preserve it longer, but the first automatically sliced commercial loaves were produced on july 6, 1928, in chillicothe, missouri, using a machine invented by otto rohwedder, an iowa-born, missouri-based jeweler.[1] pre-sliced bread would indeed dry out, were it not for another 20th century technology: the plastic bag. bread could now be pre-sliced, and if the enclosing bag remains sealed as much as possible, the bread will remain soft and fresh for longer than if sitting unwrapped on a shelf or enclosed in a bread box that is not air-tight. sealed packaging meant bread could also be sold on store shelves and eliminate frequent trips to a bakery.

sealing bread in a plastic bag had another effect: the moisture in the loaf will re-distribute into the crust and soften it, which is sometimes more pleasing in a sandwich - especially for children whose teeth might not yet be strong enough to tear through a hard crust. a homemade loaf of bread can be sealed in a bag overnight and the crust will become soft like store-bought sandwich bread.

these were novel changes in how bread was produced and sold, which led to the coining of the phrase “the greatest thing since sliced bread.”

Answer from: Quest

c-14 is carbon-14, or radiocarbon. it is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons.

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