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bonufazy [111]
3 years ago
14

How many controls or controlled variables can there be in an experiment

Chemistry
1 answer:
notsponge [240]3 years ago
3 0

i would say 35 i think

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Pentaborane-9, B5H9, is a colorless, highly reactive liquid that will burst into flame when exposed to oxygen. The reaction is 2
mina [271]

<u>Answer:</u> The amount of energy released per gram of B_5H_9 is -71.92 kJ

<u>Explanation:</u>

For the given chemical reaction:

2B_5H_9(l)+12O_2(g)\rightarrow 5B_2O_3(s)+9H_2O(l)

The equation used to calculate enthalpy change is of a reaction is:  

\Delta H^o_{rxn}=\sum [n\times \Delta H^o_f_{(product)}]-\sum [n\times \Delta H^o_f_{(reactant)}]

The equation for the enthalpy change of the above reaction is:

\Delta H^o_{rxn}=[(5\times \Delta H^o_f_{(B_2O_3(s))})+(9\times \Delta H^o_f_{(H_2O(l))})]-[(2\times \Delta H^o_f_{(B_5H_9(l))})+(12\times \Delta H^o_f_{(O_2(g))})]

Taking the standard enthalpy of formation:

\Delta H^o_f_{(B_2O_3(s))}=-1271.94kJ/mol\\\Delta H^o_f_{(H_2O(l))}=-285.83kJ/mol\\\Delta H^o_f_{(B_5H_9(l))}=73.2kJ/mol\\\Delta H^o_f_{(O_2(g))}=0kJ/mol

Putting values in above equation, we get:

\Delta H^o_{rxn}=[(5\times (1271.94))+(9\times (-285.83))]-[(2\times (73.2))+(12\times (0))]\\\\\Delta H^o_{rxn}=-9078.57kJ

We know that:

Molar mass of pentaborane -9 = 63.12 g/mol

By Stoichiometry of the reaction:

If 2 moles of B_5H_9 produces -9078.57 kJ of energy.

Or,

If (2\times 63.12)g of B_5H_9 produces -9078.57 kJ of energy

Then, 1 gram of B_5H_9 will produce = \frac{-9078.57kJ}{(2\times 63.12)}\times 1g=-71.92kJ of energy.

Hence, the amount of energy released per gram of B_5H_9 is -71.92 kJ

8 0
3 years ago
What did you include in your response? Check all that apply.
Aliun [14]

Answer:

Without corals, the algae are not protected and cannot perform photosynthesis.

5 0
3 years ago
Read 2 more answers
Read the selection from the section "Molecules In Motion." The molecules in the hot soup are traveling faster overall than they
Hoochie [10]

Answer: The author used the word "conversely" because the first statement he made is in CONTRAST to the second statement he made.

Explanation:

Matter is made up of atoms or molecules that are in constant motion. The motion of these tiny particles ( molecules) gives the object energy. The movement of these molecules depends on the state of matter which includes

--> GASEOUS STATE: Here, the particles are completely free to move and are always in motion.

--> LIQUID STATE: particles in this state slide by one another and are always in motion.

--> SOLID STATE: particles in this state are held tightly together but are always in motion.

Also, the molecules in motion are greatly affected by temperature changes. Increase in temperature will cause the particles in the liquid to move faster. Such is seen when soup is heated, the molecules travel faster than before. But the OPPOSITE is seen in an ice cube. This is because the ice cube is in solid state and of a lower temperature.

7 0
2 years ago
Compare the amount of heat required to vaporize a 200.-gram sample of H2O(ℓ) at its boiling point to the amount of heat required
stira [4]
The enthalpy of vaporization of H2O is higher than the enthalpy of fusion of H2O, therefore vaporizing the same mass of H2O would require more heat/energy than melting the same mass of H2O.
6 0
3 years ago
A student needed to make 100.0 mL of 0.20M NaOH solution. How many grams of sodium hydroxide does the student need to weigh out
GuDViN [60]

Answer:

0.08 g

Explanation:

100.0 mL = 0.10 L

Multiply the volume by the molarity to find moles.

0.10 L × 0.20 M = 0.002 mol

Convert moles to grams.

0.002 mol × 40 g/mol = 0.08 g

4 0
3 years ago
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