I think it’s B not rlly sure
Answer:
Evaporation
Explanation:
Heat makes molecules move and eventually evaporate.
Answer: If a substance has a boiling point of 
then it is true that it will also change from a gas to a liquid at 78 °C while the gas loses energy.
Explanation:
The temperature at which vapor pressure of a liquid substance becomes equal to the atmospheric pressure is called boiling point of substance.
At the boiling point, liquid phase and vapor phase remains in equilibrium.
This means that as liquid phase changes into vapor phase and also vapor phase changes into liquid phase at the boiling point.
Thus, we can conclude that if a substance has a boiling point of then it is true that it will also change from a gas to a liquid at 78 °C while the gas loses energy.
1.34 L of HF
Explanation:
We have the following chemical reaction:
Sn (s) + 2 HF (g) → SnF₂ (s) + H₂ (g)
First we calculate the number of moles of SnF₂:
number of moles = mass / molecular weight
number of moles of SnF₂ = 5 / 157 = 0.03 moles
From the chemical reaction we see that 1 mole of SnF₂ are produced from 2 moles of SnF₂. This will mean that 0.03 moles of SnF₂ are produced from 0.06 moles of HF.
Now at standard temperature and pressure (STP) we can use the following formula to calculate the volume of HF:
number of moles = volume / 22.4 (L/mole)
volume of HF = number of moles × 22.4
volume of HF = 0.06 × 22.4 = 1.34 L
Learn more about:
problems with gases at STP
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