Amixture of 1.374 g of h_2 and 70.31 g of br_2 is heated in a 2.00 l vessel at 700 k. these substances react as follows: h_2(g) + br_2(g) 2 hbr(g) at equilibrium the vessel is found to contain 0.566 g of h_2. calculate the equilibrium concentration of hbr. express your answer using three significant figures. use the following values in your calculations: molar mass of h_2 = 2.0159 g/mol and molar mass of br_2 = 159.81 g/mol. do not round any of your values in your calculations to the requested number of significant figures until the very last step.

0.400 M

Explanation:

The reaction given is

H₂(g) + Br₂(g) ⇄ 2HBr(g)

So, the stoichiometry is 1 mol of H₂ for 1 mol of Br₂ to form 2 moles of HBr.

By the molas masses given, the number of moles of each compound is (mass/molar mass):

nH₂ = 1.374/2.0159 = 0.681581427 mol

nBr₂ = 70.31/159.81 = 0.439959952 mol

The number of moles of H₂ in the equilibrium will be:

nH₂e = 0.566/2.0159 = 0.280767895 mol

So the number of moles that reacts is the initial less the equilibrium:

n = 0.400813531 mol

For the stoichiometry, the number of moles that is formed of HBr must be double, which will be the number of moles in equilibrium:

nHBr = 0.801627063

The molar concentration is the number of moles divided by the volume:

0.801627063/2.00

0.400 M

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.”