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sergij07 [2.7K]
3 years ago
13

What is not true about most combustion reactions?

Chemistry
1 answer:
vazorg [7]3 years ago
6 0
Combustion, or burning,[1] is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combustion in a fire produces a flame, and the heat produced can make combustion self-sustaining. Combustion is often a complicated sequence of elementary radical reactions. Solid fuels, such as wood and coal, first undergo endothermic pyrolysis to produce gaseous fuels whose combustion then supplies the heat required to produce more of them. Combustion is often hot enough that incandescent light in the form of either glowing or a flame is produced. A simple example can be seen in the combustion of hydrogen and oxygen into water vapor, a reaction commonly used to fuel rocket engines. This reaction releases 242 kJ/mol of heat and reduces the enthalpy accordingly (at constant temperature and pressure):

2H
2(g) + O
2(g) → 2 H2O(g)

Combustion of an organic fuel in air is always exothermic because the double bond in O2 is much weaker than other double bonds or pairs of single bonds, and therefore the formation of the stronger bonds in the combustion products CO2 and  H2O results in the release of energy.[2] The bond energies in the fuel play only a minor role, since they are similar to those in the combustion products; e.g., the sum of the bond energies of CH4 is nearly the same as that of CO2. The heat of combustion is approximately -418 kJ per mole of O2 used up in the combustion reaction, and can be estimated from the elemental composition of the fuel.[2]

Uncatalyzed combustion in air requires fairly high temperatures. Complete combustion is stoichiometric with respect to the fuel, where there is no remaining fuel, and ideally, no remaining oxidant. Thermodynamically, the chemical equilibrium of combustion in air is overwhelmingly on the side of the products. However, complete combustion is almost impossible to achieve, since the chemical equilibrium is not necessarily reached, or may contain unburnt products such as carbon monoxide, hydrogen and even carbon (sootor ash). Thus, the produced smoke is usually toxic and contains unburned or partially oxidized products. Any combustion at high temperatures in atmospheric air, which is 78 percent nitrogen, will also create small amounts of several nitrogen oxides, commonly referred to as NOx, since the combustion of nitrogen is thermodynamically favored at high, but not low temperatures. Since combustion is rarely clean, flue gas cleaning or catalytic converters may be required by law.

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Calculate the amount of water required to prepare 500g of 2.5% solution of sugar.
Snowcat [4.5K]

(i) We start by calculating the mass of sugar in the solution:

mass of sugar = concentration × solution mass

mass of sugar = 2.5/100 × 500 = 12.5 g  

Then now we can calculate the amount of water:

solution mass = mass of sugar + mass of water

mass of water =  solution mass - mass of sugar

mass of water = 500 - 12.5 = 487.5 g

(ii) We use the following reasoning:

If       500 g solution contains 12.5 g sugar

Then    X g solution contains 75 g sugar

X=(500×75)/12.5 = 3000 g solution

Now to get the amount of solution in liters we use density (we assume that is equal to 1):

Density = mass / volume

Volume = mass / density

Volume = 3000 / 1 = 3000 liters of sugar solution

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3 years ago
A strong acid is one that:
HACTEHA [7]

Answer:

A strong acid completely ionizes in water.

5 0
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What is a chemical change
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Which statement below about contrasting Hb and Mb is FALSE?
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Answer:

C. Hb binds O2 more tightly than Mb.

Explanation:

<u>Hb and Mb are both oxygen carrier protiens which contain the heme group. Hb has 4 heme units in 1 moleucle which work via coperative effect. On the other hand, Mb has only one heme unit. </u>

<u>From above theory, statement A and B are correct.</u>

<u>Although the heme group of the Mb is identical to those of Hb, Mb has a higher affinity for carrying oxygen than hemoglobin.</u>

<u>Hence, Statement C is wrong.</u>

Thats why the function of hemoglobin is to transport oxygen and that of myoglobin is to store oxygen.

<u>When a curve is plotted between oxygen accepted and the pressure of the oxygen, Hb shows sigmoidal, whereas Mb shows hyperbolic oxygen saturation curves.</u><u> The statement D is correct.</u>

<u>Bohr effect and various factors decribe the statement : Hb-oxygen binding is dependent on physiological changes in pH, whereas Mb-oxygen binding is not. </u><u>The  statement E is also correct.</u>

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, Hydrocarbons are compounds that contain(1) carbon, only(2) carbon and hydrogen, only(3) carbon, hydrogen, and oxygen, only(4)
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Hydrocarbons are compounds formed by only hydrogen atoms and carbon.

Answer (2)

hope this helps!
4 0
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