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3 years ago

C.) Is heating of cobalt (ii) chloride crystals a chemical change or a physical change (Imk)

1 answer:

8 0

Answer: Heating the hydrated forms of cobalt chloride reverses the reactions above, returning cobalt chloride to the blue, water-free, or anhydrous, state. Water is "liberated" in these reactions, known as dehydration reactions.

Explanation:

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The total surface area for the Asia consisting of forest, cultivated land, grass land, and desert is approximately 4.46 x 107 km

tester [92]

Explanation:

We calculate the amount of carbon fixed as follows.

$455 \times 10^{3} kg/km^{2} \times 4.46 \times 10^{7} km^{2}$

= $2029.3 \times 10^{10}$ kg

$\Delta H_{f}_{C_{6}H_{12}O_{6}}$ = -1273.1 kJ/mol

$\Delta H_{f}_{CO_{2}}$ = -393.5 kJ/mol

$\Delta H_{f}_{H_{2}O}$ = -285.8 kJ/mol

Hence, total $\Delta H$ reaction will be as follows.

$\Delta H_{rxn} = (\Delta H_{f}_{C_{6}H_{12}O_{6}}) - 6(\Delta H_{f}_{CO_{2}}) - 6(\Delta H_{f}_{H_{2}O})$

= $-1273.1 kJ/mol - (6 \times 393.5 kJ/mol) - (6 \times 285.8 kJ/mol)$

= 2802.7 kJ/mol

Therefore, calculate the number of moles of fixed carbon as follows.

$n_{c, fixed} = \frac{m_{c, fixed}}{\text{Molar mass of C in kg/mol}}$

= $\frac{4.55 \times 10^{5}kg km^{-2} year^{-1}}{12.01 \times 10^{-3} kg/mol}$

= $3.786 \times 10^{7} mol km^{-2} year^{-1}$

Thus, we can conclude that the annual enthalpy change resulting from the photosynthetic carbon fixation over the land surface is $3.786 \times 10^{7} mol km^{-2} year^{-1}$ .

7 0

3 years ago

How much 10.0 M HNO must be added to 1.00 L of a buffer that is 0.0100 M acetic acid and 0.100 M sodium acetate to reduce the pH

Naya [18.7K]

Explanation:

It is given that molarity of acetic acid = 0.0100 M

Therefore, moles of acetic acid = molarity of acetic acid × volume of buffer

Moles of acetic acid = 0.0100 M × 1.00 L

= 0.0100 mol

Similarly, moles of acetate = molarity of sodium acetat × volume of buffer

= 0.100 mol

When $HNO_{3}$ is added, it will convert acetate to acetic acid.

Hence, new moles acetic acid = (initial moles acetic acid) + (moles $HNO_{3}$ )

= 0.0100 mol + x

New moles of sodium acetate = (initial moles acetate) - (moles $HNO_{3}$ )

= 0.100 mol - x

According to Henderson - Hasselbalch equation,

pH = $pK_{a} + log\frac{[conjugate base]}{[weak acid]}$

pH = $pKa + log\frac{(new moles of sodium acetate)}{(new moles of acetic acid)}$

4.95 = 4.75 + $log\frac{(0.100 mol - x)}{(0.0100 mol + x)}$

$log\frac{(0.100 mol - x)}{(0.0100 mol + x)}$ = 4.95 - 4.75

= 0.20

$\frac{(0.100 mol - x)}{(0.0100 mol + x)}$ = antilog (0.20)

= 1.6

Hence, x = 0.032555 mol

Therefore, moles of $HNO_{3}$ = 0.032555 mol

volume of $HNO_{3}$ = $\frac{moles HNO_{3}}{molarity of HNO_{3}}$

= $\frac{0.032555 mol}{10.0 M}$

= 0.0032555 L

or, = 3.25 (as 1 L = 1000 mL)

Thus, we can conclude that volume of $HNO_{3}$ added is 3.26 mL.

5 0

3 years ago

Plasma is often in stars, which are likely to contain?

elena-s [515]

Below are the choices that can be found from other sources:

A) elements
B) ions
C) molecules
D) neutrons

the answer is ions.

A Star and hence our Sun, is an almost entirely ionized ball of plasma, consisting of electrons and ions, in which there is hardly any gas (neutral atoms). The movement of the plasma produces strong magnetic fields and corresponding electric currents.

6 0

4 years ago

The layered structures made of calcium carbonate by precambrian cyanobacteria are called _____.

Valentin [98]

stromatolites I think

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3 years ago

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How many grams of iron are needed to react with 3.00 g of sulfur?

Wewaii [24]

I need really help with my work schedule for tomorrow

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