Chemistry help!? please help me?

Question

please help me with these 3 questions, i am having a lot of trouble trying to figure them out?

1.) The Space Shuttle's rocket boosters use hydrogen and oxygen, which combine to form water as fuel. The balanced chemical equation of this exothermic reaction is?

a. 2H2(g) + O(g) ––> 2H2O(g)

b. 2H2(g) +3O(g) ––>3H2O(g)

c. 2H(g) + O(g) ––> 2H2O(g)

d. 2H2(g) + O2(g)––> 2H2O(g)

2.) During an experiment, a metal and an excess of fluorine gas were placed into a combustion chamber at a temperature of 1800°C. The temperature in the sealed chamber continued to rise to 2100°C. After the reaction stopped, a brittle white substance, which dissolved in water, was extracted from the chamber. From this evidence one could conclude that this reaction can be classified as?

a. endothermic formation reaction

b. exothermic formation reaction

c. endothermic decomposition reaction

d. exothermic decomposition reaction

3.) State the law of conservation of mass and explain how a balanced chemical reaction equation supports the law?? in this question i know the law of conservation of mass, but i don't know how to explain how a balanced chemical reaction equation supports the law, so please help me if u can, thank you.

Answer 1

1.  The correct balanced reaction is choice d, since Hydrogen gas and Oxygen gas are most stable as diatomic gases (H(g) and O(g) are not stable).

2.  Since the reaction results in an increase in temperature, energy is released during the reaction (exothermic).  The product is a new substance which can dissolve in water, so it must be either polar or ionic, which would result if fluorine binds to the metal.  This leads me to believe that this reaction is a formation reaction.  Answer choice: b.

3.  A balanced chemical reaction demonstrates that whatever atoms go into a reaction as reactants come out of the other side as products.  No additional atoms appear from nothing (matter is not created) and no atoms vanish during the reaction (or destroyed).

Hope this helps.

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Additional comments:

Having fluorine in excess does not necessarily mean the reaction must be a formation reaction.  The "in excess" just means all of the metal is able to react, no matter how many moles of fluorine are required to react with one mole of metal in order to form the product.

Answer 2

1) D - its the only balanced one

2) D - heat is given out so exo. Fluorine in excess so CANT be formation