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3 years ago

12

HELP!!!!!!!!!!!! ASAP!!!!!!!!!!!!!!!!!!! CHEMISTRY TEST!!!!!!!!!!!!!! 53 POINTS

1 answer:

lbvjy [14]3 years ago

3 0

Answer:

9.1 KJ

Explanation:

First we must find the number of moles of HBr involved;

number of moles of HBr= mass of HBr/ molar mass of HBr

But molar mass of HBr= 80.91 g/mol

Given mass of HBr from the question= 20.1g

Hence;

Number of moles of HBr= 20.1 g/80.91g

Number of moles of HBr= 0.25 moles of HBr

If 2 moles of HBr has a heat of formation of 72.80KJ

Then 0.25 moles of HBr will have a heat of formation of 0.25× 72.80/2= 9.1 KJ

Therefore; 20.1 g of HBr will have a heat of formation of 9.1 KJ

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Explanation:

We are given:

Mass of $CO_2$ = 18.95 g

Mass of $H_2O$ = 7.759 g

Molar mass of carbon dioxide = 44 g/mol

Molar mass of water = 18 g/mol

For calculating the mass of carbon:

In 44g of carbon dioxide, 12 g of carbon is contained.

So, in 18.59 g of carbon dioxide, = $\frac{12}{44}\times 18.59=5.07g$ of carbon will be contained.

For calculating the mass of hydrogen:

In 18g of water, 2 g of hydrogen is contained.

So, in 7.759 g of water, = $\frac{2}{18}\times 7.759=0.862g$ of hydrogen will be contained.

Mass of C = 5.07 g

Mass of H = 0.862 g

Step 1 : convert given masses into moles.

Moles of C = $\frac{\text{ given mass of C}}{\text{ molar mass of C}}= \frac{5.07g}{12g/mole}=0.422moles$

Moles of H= $\frac{\text{ given mass of H}}{\text{ molar mass of H}}= \frac{0.862g}{1g/mole}=0.862moles$

Step 2 : For the mole ratio, divide each value of moles by the smallest number of moles calculated.

For C = $\frac{0.422}{0.422}=1$

For H = $\frac{0.862}{0.422}=2$

The ratio of C : H = 1: 2

Hence the empirical formula is $CH_2$ .

The empirical weight of $CH_2$ = 1(12)+2(1)= 14 g.

The molecular weight = 56.1 g/mole

Now we have to calculate the molecular formula.

$n=\frac{\text{Molecular weight }}{\text{Equivalent weight}}=\frac{56.1}{14}=4$

The molecular formula will be= $4\times CH_2=C_4H_8$

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