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julia-pushkina [17]
3 years ago
12

A student receives 83.2 points, 44.6 points, 74.4 points, and 52.3 points on each of four tests. Determine the student’s test av

erage with the correct significant digits.
Chemistry
1 answer:
Leya [2.2K]3 years ago
3 0

Answer:

Average = 63.6

Explanation:

Average : The average of the given set of points can be calculated by dividing sum of the total point to the number of points.

Average =\frac{Sum\ of\ points}{Number\  of\ points}

The points that are given in this equation are:

83.2 , 44.6 , 74.4 , 52.3 .

These are 4 in number . So average is

Average =\frac{Sum\ of\ points}{Number\  of\ points}

Average =\frac{83.2+44.6+74.4+52.3}{4}

Average =\frac{254.5}{4}

Average =63.625

Significant digits : It is the number of digits that carry meaningful value to a measurement. The rules for counting number of significant digits are:

1. all non-zero digit are significant

2.Any zero between two non-zero are also significant.(305 = 3 significant digit )

3. Zero before the decimal are non-significant (0.003 = only 1 significant digit)

Zero after decimal are significant (3.00 has 3 significant digit)

4.Zero after non - zero digit is non significant (300 has 1 significant digit).

Significant digits in division :

The answer should have the significant digits that are least in any of number(83.2 , 44.6 , 74.4 , 52.3 )

All have = 3 significant digits.

So least numner of significant digit =3

Answer should have total = 3 significant digits

So,

Average = 63.6

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Use the given data at 500 K to calculate ΔG°for the reaction
Anton [14]

Answer : The  value of \Delta G^o for the reaction is -959.1 kJ

Explanation :

The given balanced chemical reaction is,

2H_2S(g)+3O_2(g)\rightarrow 2H_2O(g)+2SO_2(g)

First we have to calculate the enthalpy of reaction (\Delta H^o).

\Delta H^o=H_f_{product}-H_f_{reactant}

\Delta H^o=[n_{H_2O}\times \Delta H_f^0_{(H_2O)}+n_{SO_2}\times \Delta H_f^0_{(SO_2)}]-[n_{H_2S}\times \Delta H_f^0_{(H_2S)}+n_{O_2}\times \Delta H_f^0_{(O_2)}]

where,

\Delta H^o = enthalpy of reaction = ?

n = number of moles

\Delta H_f^0 = standard enthalpy of formation

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

\Delta H^o=[2mole\times (-242kJ/mol)+2mole\times (-296.8kJ/mol)}]-[2mole\times (-21kJ/mol)+3mole\times (0kJ/mol)]

\Delta H^o=-1035.6kJ=-1035600J

conversion used : (1 kJ = 1000 J)

Now we have to calculate the entropy of reaction (\Delta S^o).

\Delta S^o=S_f_{product}-S_f_{reactant}

\Delta S^o=[n_{H_2O}\times \Delta S_f^0_{(H_2O)}+n_{SO_2}\times \Delta S_f^0_{(SO_2)}]-[n_{H_2S}\times \Delta S_f^0_{(H_2S)}+n_{O_2}\times \Delta S_f^0_{(O_2)}]

where,

\Delta S^o = entropy of reaction = ?

n = number of moles

\Delta S_f^0 = standard entropy of formation

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

\Delta S^o=[2mole\times (189J/K.mol)+2mole\times (248J/K.mol)}]-[2mole\times (206J/K.mol)+3mole\times (205J/K.mol)]

\Delta S^o=-153J/K

Now we have to calculate the Gibbs free energy of reaction (\Delta G^o).

As we know that,

\Delta G^o=\Delta H^o-T\Delta S^o

At room temperature, the temperature is 500 K.

\Delta G^o=(-1035600J)-(500K\times -153J/K)

\Delta G^o=-959100J=-959.1kJ

Therefore, the value of \Delta G^o for the reaction is -959.1 kJ

3 0
3 years ago
Elements in the first column of the periodic table belong to the alkali family. Name the alkali metals.
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Lithium, sodium, potassium, rubidium, cesium, and francium
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1. Analysis of an unknown substance formerly used in rocket fuel reveals a composition of 93.28% nitrogen and 6.72% hydrogen by
Nitella [24]

Answer:

The formula of the compound is:

N2H2

Explanation:

Data obtained from the question:

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Hydrogen (H) = 6.72%

Next, we shall determine the empirical formula for the unknown compound. This is illustrated below:

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Divide by their molar mass

N = 93.28 /14 = 6.663

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Divide by the smallest

N = 6.663 / 6.663 = 1

H = 6.72 /6.663 = 1

Therefore, the empirical formula is NH.

Now, we can obtain the formula of the compound as follow:

The formula of a compound is simply a multiple of the empirical formula.

[NH]n = 30.04

[14 + 1]n = 30.04

15n = 30.04

Divide both side by 15

n = 30.04/15

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Therefore, the formula of the compound is:

[NH]n => [NH]2 => N2H2

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