[peterpan1372]

Hello,

Sodium reacts with water, producing hydrogen.

My question:

is the equation right? If not, why?

Na + H20 -> H2 + NaO

[Arkcon]

Nope.  Its not really correct.  You've written a balanced equation, with the same numbers of atoms on both sides, but one product is wrong.  Generally, in a high school problem, they tell you all products.  So, can you check a text book, for the correct products of this reaction?

[peterpan1372]

no, I am preparing for BMAT. I am not at high school, but at Uni. What is wrong about my equation?

[peterpan1372]

I have an inkling that it must be NaOH.... but why? we only have one O in H20 and with the hydrogen on the right side its perfectly balanced out...

[Arkcon]

Often, we use the state of products and reactants.  If you're mixing everything in water, your product, NaO, will react further in water.  So your product is wrong.  You may need to review some basic textbooks in order to be ready for a standardized test.  Start with the practice tests, and see if the guide to answers direct you to the concepts you need to brush up on.

[Arkcon]

I have an inkling that it must be NaOH.... but why? we only have one O in H20 and with the hydrogen on the right side its perfectly balanced out...

Good work.  The BMAT expects you to have had a beginning knowledge of this topic.  Review the textbook where you learned this topic, to see what you may have forgotten, and see how well you can do on BMAT practice exams afterward.

[Corribus]

It's true that all chemical reaction equations must be balanced, but not all balanced chemical reaction equations are likely to happen. Being able to discriminate between likely and unlikely reactions takes a deeper understanding of chemistry and, often, thermodynamics. In this case, NaO is an unlikely product because it requires sodium or oxygen to take on very unlikely oxidation states (+2 for sodium or -1 for oxygen). Sodium oxide does occur, but with formula Na₂O, reflecting the more common oxidation states of oxygen (-2) and sodium (+1). However in water the oxide spontaneously forms NaOH, which is a more thermodynamically stable end product. Beginners to chemistry wouldn't necessarily be able to predict these kinds of things, but you will start to learn rules of thumb that should help you predict the likely formulae of common compounds, e.g., first column elements tend to be +1, second column elements tend to be +2, oxygen is usually -2, halogens -1, etc.

[billnotgatez]

@Corribus

It is interesting that many of the results from GOOGLE for this problem stress
That water can also be thought of as H⁺ and OH^-
and solve the balancing that way

[Arkcon]

Also, sometimes we include the state of matter of the reactants:

Na(s)+H₂O(l) H₂(g) + NaO

Well, NaO ... what?

NaO(s)  , as an insoluble solid?  Is that the properties?  Or NaO(aq), is it water soluble?  We have to know.