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3 years ago

Which of the following processes releases heat? Evaporation Freezing Melting Sublimation . I know for sure it is not freezing.

2 answers:

Ivan3 years ago

6 0

Freezing process release heat that is the process is exothermic . In addition condensation process also is exothermic. When substance losses heat energy the attractive force between atom slow down and hence reduces their mobility.Example when water turn to a ice cubes the reaction releases heat energy.

gayaneshka [121]3 years ago

4 0

During freezing heat will be released. Normally we wont think like that ,but the reality is during freezing the heat get released. the liquid water will have more energy than the frozen water .so during this transition the energy of the water get released as the latent heat. Basically when we need to reduce the temperature ie. freezing a substance, the heat already absorbed in the substance should be released out of the substance.

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How many grams of sodium fluoride should be added to 300. mL of 0.0310 M of hydrofluoric acid to produce a buffer solution with

Kisachek [45]

Answer : The mass of sodium fluoride added should be 0.105 grams.

Explanation : Given,

The dissociation constant for HF = $K_a=6.8\times 10^{-4}$

Concentration of HF (weak acid)= 0.0310 M

First we have to calculate the value of $pK_a$ .

The expression used for the calculation of $pK_a$ is,

$pK_a=-\log (K_a)$

Now put the value of $K_a$ in this expression, we get:

$pK_a=-\log (6.8\times 10^{-4})$

$pK_a=4-\log (6.8)$

$pK_a=3.17$

Now we have to calculate the concentration of NaF.

Using Henderson Hesselbach equation :

$pH=pK_a+\log \frac{[Salt]}{[Acid]}$

$pH=pK_a+\log \frac{[NaF]}{[HF]}$

Now put all the given values in this expression, we get:

$2.60=3.17+\log (\frac{[NaF]}{0.0310})$

$[NaF]=0.00834M$

Now we have to calculate the moles of NaF.

$\text{Moles of NaF}=\text{Concentration of NaF}\times \text{Volume of solution}=0.00834M\times 0.300L=0.0025mole$

Now we have to calculate the mass of NaF.

$\text{Mass of }NaF=\text{Moles of }NaF\times \text{Molar mass of }NaF=0.0025mole\times 42g/mole=0.105g$

Therefore, the mass of sodium fluoride added should be 0.105 grams.

4 0

3 years ago

What the sample will look like after the temperature is increased from 300 K to 450 KK at constant pressure?

sleet_krkn [62]

Answer:

The sample will look expanded and occupy more space.

Explanation:

Since, the pressure is constant here, but the temperature is changed. Therefore, according to Charles' Law Volume is directly proportional to Temperature, provided the pressure is kept constant. Mathematically:

V1/T1 = V2/T2

V1 = (T1/T2)(V2)

V1 = (300 k/450 k)(V2)

V1 = (0.67)V2

The equation indicates that The fina volume of the gas V2 will be greater than the initial volume V1. Thus, sample will look expanded and occupy more space than the previous state.

5 0

3 years ago

Assume reaction N (g )space plus O (g )rightwards arrow N O (g )occurs in high layers of the atmosphere. What is the H subscript

8090 [49]

Answer:

Kindly check the explanation section.

Explanation:

From the description given in the question above, that is '' H subscript f to the power of degree of the reaction" we have that the description matches what is known as the heat of formation of the reaction, ∆fH° where the 'f' is a subscript.

In order to determine the heat of formation of any of the species in the reaction, the heat of formation of the other species must be known and the value for the heat of reaction, ∆H(rxn) must also be known. Thus, heat of formation can be calculated by using the formula below;

∆H(rxn) = ∆fH°( products) - ∆fH°(reactants).

That is the heat of formation of products minus the heat of formation of the reaction g specie(s).

Say heat of formation for the species is known as N(g) = 472.435kj/mol, O(g) = 0kj/mol and NO = unknown, ∆H°(rxn) = −382.185 kj/mol.

−382.185 = x - 472.435kj/mol = 90.25 kJ/mol

5 0

3 years ago

A family from Ottawa turned off the heat before flying to Florida for a winter holiday. When they came home, all of their water

NeX [460]

Explanation:

In the extreme winters , the water inside pipes freeze, on freezing it's(water molecule) density decreases and volume increases and therefore, the ice then expands and pushes the water towards the faucet, causing high pressure buildup in the pipe and after a limit the pipe burst. This is what happened to the family in Ottawa, where winters are chilly.

5 0

3 years ago

Read 2 more answers

4. If the earth were to heat up by 3 degrees, approximately how much would the sea level rise?

Ksju [112]

The sea level would rise by some 50 meters.

Explanation:

If the earth's temperature increases by 3 degrees the north and south pole would experience the ice melt at high speed.

The life will get difficult on the plains.

The extinction of some species will happen.

The sea level would rise by 50 meters. The increased sea level will cause depletion of habitat from plants and animals.

The floods will occur, land erosion, soil for agriculture land will get contaminated with the salt.

8 0

3 years ago