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3 years ago

Which of the following processes is exothermic?

Chemistry

2 answers:

Elodia [21]3 years ago

8 0

Answer:

a. The reaction associated with DHºf for an ionic compound

Explanation:

An exothermic process is a process that loses heat for the surroundings, so the temperature of the system must decrease, and ΔH must be negative.

DHºf or ΔHºf of an ionic compound is always negative because the final energy is always lower than the initial. It happens because of the stability of the bond, the system wants a lower energy state to be stable.

The ionization of a lithium atom occurs with the gain of energy, which is given to the electron, so it may give off the atom. So it's an endothermic process.

To change the state of a solid to a gas (sublimation), the compound must gain heat, its temperature must increase, so it's always an endothermic process.

To break a covalent bond it's necessary the gain of energy, so it's an endothermic process.

Korvikt [17]3 years ago

5 0

Answer:A

Explanation:

The enthalpy change of formation for an ionic compound is calculated from the Born-Haber cycle. Using the Hess law of constant heat summation. The result is always negative (exothermic) because energy is given out when the new lattice is formed.

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How often do girls normally experience menstruation a.once every 30 days b. once every 29 c.once every 28 d.once every 27

kramer

Answer:

i think answer is a, every 30 days

5 0

3 years ago

Read 2 more answers

Consider the reaction between reactants s and o2: 2s(s)+3o2(g)→2so3(g)if a reaction vessel initially contains 7 mols and 9 mol o

nadya68 [22]

Answer: -

1 mol

Explanation: -

Number of moles of Sulphur S = 7

Number of moles of O2 = 9

The balanced chemical equation for the reaction is

2S (s)+3 O2 (g)→2SO3(g)

From the above reaction we can see that

3 mol of O2 react with 2 mol of S

9 mol of O2 will react with $\frac{2 mol S x 9 mol O2}{3 mol O2}$

= 6 mol of S

Unreacted S = 7 - = 1 mol.

If a reaction vessel initially contains 7 mol S and 9 mol O2

1 mole of s will be in the reaction vessel once the reactants have reacted as much as possible

6 0

3 years ago

The equation shows one mole of ethanol fuel being burned in oxygen. Convert the energy released into its equivalent mass. C2H5OH

lana [24]

Answer:

47.9 g of ethanol

Explanation:

Combustion is a chemical reaction in which a substance reacts with oxygen to produce heat and light. Combustion reactions have been very useful as a source of energy. Ethanol is now burnt for energy purposes as a fuel. Ethanol has even been proposed as a possible alternative to fossil fuels.

Since 1 mole of ethanol when combusted releases 1367 kJ/mol of energy

x moles of ethanol releases 1418 kJ/mol.

x= 1 × 1418 kJ/mol/ 1367 kJ/mol

x= 1.04 moles of ethanol.

Mass of ethanol = number of moles × molar mass

Molar mass of ethanol = 46.07 g/mol

Mass of ethanol = 1.04 moles × 46.07 g/mol

Mass of ethanol= 47.9 g of ethanol

7 0

2 years ago

Why is mercury the only metal to have been used in thermometers

MArishka [77]

I think because its the only one to be liquid at normal temperatures.

6 0

3 years ago

What element has 4 valence electrons and 5 electron shells?

marta [7]

Answer: Tin (Sn)

Explanation: The electron configuration for tin (Sn) is shown in the picture. It's last electrons are:

5s^2 4d^10 5p^2

The valence electrons are in the 5th electron shell and include 2 each in the 5s and 5p orbitals.

8 0

3 years ago