What mass of methanol is combusted in a reaction that produces 112 L of Co2 at STP?
A. 112g
B. 81.6g
C. 64.1g
D. 160g

Answer

D 160g

Explanation:

Write the equation:

Combustion reactions use oxygen and release water and heat, so

  CH₃OH(g) + O₂(g) → CO₂(g) + H₂O(g)

Balance that:

  2CH₃OH(g) + 3O₂(g) → 2CO₂(g) + 4H₂O(g)

Find moles of carbon dioxide:

We need to know the number of moles of CO₂. This rxn is at STP, so at STP one mole of gas = 22.4 liters.

  112 L * 1 mol/22.4 L = 5 mol CO₂

Find moles of methanol:

Based on the chemical equation, for every 2 mol methanol, there are 2 mol carbon dioxide. So for every 5 mol carbon dioxide, there are 5 mol methanol!

  5 mol CO₂ = 5 mol CH₃OH

Molar mass of methanol: 12.01 + 3*1.008 + 16.00 + 1.008 = 32.04 g/mol

Moles of methanol: 5 mol * 32.04 g/mol = 160.2 g methanol

≈ 160 mol methanol

it can be observed without changing the identity of the object.

it depends on what substance you're talking about as well as many other factors. in quantum mechanics, the observation of particles affects the observers ability to measure certain properties. for example: you can know the velocity of a particle, but you can't know it's position; or you can know it's position, but not it's velocity. it's like trying to find out where a grain of sand is by throwing other grains of sand at it. once you find out where it is, it's been moved. it's also like trying to find an answer to the question of whether or not a tree falling in a forest makes a sound if nobody is there to hear it. paradoxically, the only way to find out is to be there and hear it.