~40 answer quickly! ~ 1) chemical substances: 1- cuo 2- o2 3- cu2o 4- n2 5- c2h5nh2 6- li2o which substances in the list can be some of the reactants and products in the same combustion reaction? a) 1, 2, and 4 b) 2, 3, and 6 c) 2, 4, and 5 d) 1, 2, and 5 2) which of the following is a valid combustion reaction? a) c2h4 + o2 → 2c + 2h2o b) mg + h2o → mgo + h2 c) n2 + 2o2 → 2no2 d) s + o2 → s + h2o 3) when calcium metal (ca) reacts with oxygen gas (o2), it produces the ionic compound calcium oxide (cao). write the balanced equation for this reaction. then, explain if this process meets the requirements to be considered a redox reaction.

So,

1. Notice that CuO, Cu2O, and Li2O are already oxides, meaning they are products of combustion reactions.  They cannot be both products and reactants in a single combustion reaction.  At this point, the only choice that does not include 1, 3, or 6 is C.  The only way oxygen (or any substance) can "be" in both the products and reactants is if there is excess of that substance.  (nevertheless, strictly speaking, the balanced equation would not contain the same species on both sides as they would cancel out).

2. Combustion reactions always are: oxidizable substance + oxygen --> oxidized substance

Combustion of hydrocarbons always produces water and carbon dioxide.

B is ruled out by the first criterion.

D is not even balanced.

A is ruled out by the second criterion.

The only remaining answer is C.

3. First, put the raw species in the reaction equation:

Next, put a 1/2 in front of the oxygen to balance it.  The balanced equation is:

To determine if this is a redox reaction, see if there is any electron transfer.  The oxidation number of Ca changes from +0 to +2, while that of oxygen changes from +0 to -2.  Therefore, this is a redox reaction.

relative humidity is a measure of the amount of moisture in the air relative to the total amount of moisture the air can hold.

so d

i just got this problem. it's 90.3