# 71

## Explanations

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## Discussion List

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Secondary V • 10mo.

I need to explain why when we look at a laser ray, we can't see its trajectory, but when chalk powder floats in the air in front of it, we can suddenly see the ray. Can anyone help me? Thank you!

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Secondary V • 11mo.

At 25 degrees Celcius, the volume of a gas is 4,6L at a pressure of 98 kPa. What will be its volume if we triple its pressure without changing its temperature?

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Secondary V • 11mo.

How can I go from Celcius to Kelvin?

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Secondary IV • 11mo.

Hello!

The density of a gas can vary, but why?

thank you!

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Secondary IV • 11mo.

Hello, I don’t understand why salt melts ice. Could you explain it to me using the atomic model please?

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Secondary V • 11mo.

True or false - Only endothermic reactions absorb energy.

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Secondary V • 11mo.

Hi,

Why are we increasing the amount of carbon dioxide in greenhouses?

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Secondary V • 11mo.

Hello,

I have the following equation at equilibrium :

HF = H+ + F-   Kc = 6,7 x 10^-4

How do I know if the direct or the indirect reaction is favored?

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Secondary IV • 11mo.

What is the meaning of a negative temperature when using the calorimetry formula (Q=mc△t)?

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Secondary V • 11mo.

Good morning,

What is the difference between an elastic and an unelastic collision?

Thank you

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Secondary V • 11mo.

Hi Alloprof,

Do gas particles still have kinetic energy below 0 degrees Celcius?

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Secondary V • 11mo.

Hello,

What is the normal atmospheric pressure?

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Secondary IV • 11mo.

I don't understand how to solve this problem:

The atomic mass of isotope # 1 of element Ab is 73 au. The atomic mass of isotope # 2 of the element Ab is 76 au. The atomic mass of isotope # 3 of the element Ab is 74 au. The relative frequencies of each isotope are 10%, 80% and 10%, respectively.

Find the average atomic mass.

Thank you!

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Secondary IV • 11mo.

What is the periodicity of properties?

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Secondary IV • 11mo.

Emilie suffers from diabetes. Therefore, after having lunch, traces of glucose (C6H12O6) can be found in her blood. What is the total mass of sugar that can be found in her blood before it reaches a concentration of 10 mmol / L? (hint: volume of blood = 5L)

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Secondary IV • 11mo.

How do you distinguish between metals, nonmetals and metalloids in the periodic table?

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Secondary IV • 11mo.

Hi!

I have an exercise that asks me to determine the mass of sodium hydroxide (NaOH) in a basic solution by titrating it with a 1.8 mol / L acidic solution. The titration shows a neutralization volume of 30 mL for the acid and an initial volume of 20 mL for the base. I am not sure how to find the mass.

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Secondary IV • 11mo.

Hi!

I'm not sure if I understand how a titration can help us to know the concentration of a solution ... Can someone explain it to me please?

Thank you very much in advance!

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Secondary IV • 11mo.

Hi! I'm not sure I understand how pH works.

Is the higher, the more acidic?

And if for example I have a solution with a pH of 4 and another with a pH of 8, is the second solution twice as acidic as the first?

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Secondary IV • 11mo.

I have a hard time understanding how why ° C is used in the thermal energy equation Q = m * c * delta T. In many chemistry exercises, we have to use Kelvin. Thank you

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Secondary IV • 11mo.

Hello,

I have a hard time understanding how an acid-base neutralization is done in a lab. Could you explain it to me please?

Thank you so much!

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Secondary IV • 11mo.

How do the different characteristics of the elements change in the periodic table?

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Secondary IV • 11mo.

Hello, I do not understand the principle of a titration

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Secondary IV • 11mo.

Hi, I don't understand half life ???

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Secondary IV • 11mo.

Hello! I'm not sure if the Q in Q = m * c * ∆T means the heat or thermal energy?

Also, when is the Q positive and negative?

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Secondary IV • 11mo.

Hello,

Could you explain to me what are the differences between the families of the periodic table please?

Thank you so much!

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Secondary IV • 11mo.

Hello!

Can 2 elements have the same atomic number? Thank you :)

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Secondary IV • 11mo.

Hello!

I was wondering, is there a particular order in the periodic table? Because from left to right and from top to bottom the number in the box starts from 1 and goes up, but does this number mean something or is it a reference number that has been set randomly? Thanks for your time :))

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Secondary IV • 11mo.

Hi!

I was reviewing and trying to remember how to find the number of protons, electrons and neutrons in an atom? (I will put an example below) Thank you !!!

$$_{92}^{235}U$$

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Secondary V • 11mo.

How do I answer this question: how many moles of oxygen are there in 2.25 g of CO2? Thank you!