Chemistry please help I don’t understand anything

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ΔH₁₊₂₊₃ = -74.6 Kj

Video Lecture I did on these type problems... See attached

Explanation:

The vid starts with some simple Hess Law additions and progresses through to more complex systems. The problem given in your example is a bit complex as a starting point when learning about these systems, so I suggest watching the above video lecture that develops the concept from less complex systems to the more complex.

Never the less, here's your problem, but I suggest you go through the video recommended above to start with some less complex problems.

Target Rxn => C(s) + 2H₂(g) => CH₄(g)

Given:

Rxn 1 => C(s) + O₂(g) => CO₂(g)                                      ΔH₁ = -393.5 Kj

Rxn 2 => CH₄(g) + 2O₂(g) => CO₂(g) + 2H₂O(g)            ΔH₂ = -890.8 Kj

Rxn 3 => H₂(g) + 1/2O₂(g) => H₂O(l)                               ΔH₃ = -285.8 Kj

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Start by adding Rxns 1 & 2, but reverse Rxn 2, change sign of   ΔH₂ to +890.8Kj

Rxn 1 => C(s) + O₂(g) => CO₂(g)                          ΔH₁ = -393.5 Kj

Rxn 2 => CO₂(g) + 2H₂O(l) => CH₄(g) + 2O₂(g)  ΔH₂ = +890.8 Kj

Rxn 1,2 => C(s) + 2H₂O(l) => CH₄(g) + O₂(g)       ΔH₁₊₂ = +497.3 Kj

Now, Double Rxn 3 and add to Rxn 1,2 => Target Rxn

Rxn 1,2 => C(s) + 2H₂O(l) => CH₄(g) + O₂(g)        ΔH₁₊₂ = +497.3 Kj

Rxn 3   => 2H₂(g) + O₂(g) => 2H₂O(l)                   ΔH₃ = 2(-285.8) Kj = -571.6 Kj

Rxn 1,2,3 => C(s) + 2H₂(g) => CH₄(g)

ΔH₁₊₂₊₃ = (+497.3 Kj) + (-571.6 Kj) = -74.3 Kj.

fire could start, buildings collapsing, and ash falling from the sky.

explanation:

this is because the buildings or plants could catch on fire and the buildings would most likely collapse. lastly ash would fall because all the burning would cause ash to fall from the sky.

hope this .

the best answer is d because the strong cohesion is caused by the ability of water molecules to undergo hydrogen bonding.

a is incorrect because when water solidifies, it becomes   ice, which expands and occupies a bigger volume for the same mass of water in its liquid state.

b is incorrect because water has high surface tension. besides bonding to itself it hydrogen bonds to other molecules at the top decreasing possibility for breaking of attractive forces.

c is incorrect because the water molecule has oxygen which is highly electronegative and so pulls the electron pair towards itself creating a dipole moment, making the molecule polar.

e is incorrect because water has strong adhesion, ability to stick to other molecules such as glass because of this molecules having stronger hydrogen bonding than water.