Thallium(I) is oxidized by cerium(IV) as follows:
Tl+(aq) + 2Ce^4+(aq) > Tl^3+(aq) + 2Ce^3+(aq)
The elementary steps, in the presence of aqueous Mn(II), are as follows:
Step 1: Ce^4+ + Mn^2+ > Ce^3+ + Mn^3+
Step 2: Ce^4+ + Mn^3+ > Ce^3+ + Mn^4+
Step 3: Tl^+ + Mn^4+ > Tl^3+ + Mn^2+
(a) Identify the catalyst, intermediates, and the rate-determining step if the rate law is rate = k[Ce^4+][Mn^2+](b) Explain why the reaction is slow without the catalyst.(c) Classify the type of catalysis (homogeneous or heterogeneous).

A) Catalyst-Mn2+

Intermediates Mn3+ and Mn4+

Rate determining step is the reaction of Ce4+ with Mn2+

B) The reaction will be a termolecular reaction in the absence of the catalyst. It will be difficult for the two Ce2+ and Ti+ to collide in the correct orientation for reaction to occur in the absence of the catalyst hence the reaction will be slow in the absence of the catalyst.

C) Both catalyst and reactants are ions in solution hence it is a homogeneous catalysis

Explanation:

The catalyst is the specie that is regenerated at the end of a reaction. This specie is Mn2+.

Intermediates are transient species that only occur in elementary steps of a complex reaction mechanism.

The species involved in the rate determining step enter into the rate equation since the rate determining step is the slowest step in a complex reaction mechanism and determine the overall rate of reaction. The rate equation rate = k[Ce^4+][Mn^2+] confirms that the first step is the rate determining step in the overall reaction mechanism.

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.”