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3 years ago

Which of the following is not true of chemical changes?

Chemistry

2 answers:

elixir [45]3 years ago

8 0

They rarely occur at molecular levels is incorrect, actually they always occur at molecular levels

Katyanochek1 [597]3 years ago

7 0

Answer: Option (a) is the correct answer.

Explanation:

At molecular level there will be need of energy always for breaking or making of chemical bonds. Therefore, a chemical change will always occur at molecular level.

Thus, we can conclude that out of the given options, the statement a chemical change rarely occurs at the molecular level is not true of chemical changes.

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An aluminum kettle weights 1.05 kg and has a heat capacity of 0.9211 J over grams Celsius how much heat is required to increase

Serggg [28]

Answer:

64799.4 J

Explanation:

The following data were obtained from the question:

Mass (M) = 1.05 kg = 1.05 x 1000 = 1050g

Specific heat capacity (C) = 0.9211 J/g°C

Initial temperature (T1) = 23°C

Final temperature (T2) = 90°C

Change in temperature (ΔT) = T2 – T1 =

90°C – 23°C = 67°C

Heat required (Q) =....?

The heat required to increase the temperature of the kettle can b obtain as follow:

Q = MCΔT

Q = 1050 x 0.9211 x 67

Q = 64799.4 J

Therefore, 64799.4 J of heat is required to increase th temperature of the kettle from 23°C to 90°C.

4 0

3 years ago

The degree to which a weak base dissociates is given by the base-ionization constant, Kb. For the generic weak base, B B(aq)+H2O

Colt1911 [192]

Answer:

pH of a 0,245 M ammonia solution is 11,3 and percent ionization is 0,86%

Explanation:

For the equilibrium buffer of NH₃:

NH₃ + H₂O ⇄ NH₄⁺ + OH⁻; kb = 1,8x10⁻⁵

kb = [NH₄⁺] [OH⁻] / [NH₃] (1)

When 0,245 M of NH₃ is added, the equilibrium concentrations are:

[NH₃] = 0,245 - x

[NH₄⁺] = x

[OH⁻] = x.

Replacing this values in (1)

$1,8x10^{-5} = \frac{x^2}{0,245 - x}$

x² + 1,8x10⁻⁵x - 4,41x10⁻⁶ = 0

Solving for x:

x = -0,00211 No physical sense. There are not negative concentrations.

x = 0,00211 Real answer

Thus [OH⁻] in equilibrium is 0,00211 M.

As pOH = -log [OH⁻] and 14 = pH + pOH

pH of 0,00211 M is 11,3

It is possible to calculate the percent ionization thus:

Percent ionization = [OH−] equilibrium / [B] initial×100%

Replacing:

0,00211 / 0,245 × 100 = 0,86%

I hope it helps!

6 0

3 years ago

The atomic mass of oxygen is 16 and the atomic mass of hydrogen is 1. How do the current atomic masses of oxygen and hydrogen co

lina2011 [118]

- Dalton reported that seven pounds of Oxygen reacted with one pound of hydrogen to form water, but accurate modern experiment gives eight pounds to one.
- Lavoisier reported that water contains Oxygen 5.6 times more than hydrogen by weight.
- Dalton assumed that water contains 1 atom of oxygen and 1 atom of hydrogen and concluded that the relative weight of O must be 5.6 times as large as the H atom.
- By determining the relative mass we will be able to determine for example that one element has twice the mass of a second element.

5 0

3 years ago

The Î""GÂ°â€² of the reaction is âˆ’7.180 kJÂ·molâˆ’1. Calculate the equilibrium constant for the reaction at 25 Â°C.

nasty-shy [4]

Answer:

Explanation:The Î""GÂ°â€² of the reaction is âˆ’7.180 kJÂ·molâˆ’1. Calculate the equilibrium constant for the reaction at 25 Â°

5 0

3 years ago

What happens when you mix water and sugar

alexandr1967 [171]

Answer:

Mixing water and sugar produces a mixture that is called a solution. In chemistry labs, this is often an experiment used to demonstrate the solubility of a solute in a solvent. In this experiment, the solute is sugar, and water is the solvent.

5 0

3 years ago