Study the reaction.

2co + o2 → 2co2

if 3.4 moles of carbon dioxide (co2) form at the end of the reaction, how many moles of carbon monoxide (co) and oxygen gas (o2) entered the reaction?

2.0 moles of carbon monoxide and 1.0 moles of oxygen gas
6.8 moles of carbon monoxide and 3.4 moles of oxygen gas
3.4 moles of carbon monoxide and 1.7 moles of oxygen gas

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If 3.4 moles of carbon dioxide (CO2) form at the end of the reaction, 1.7 moles of oxygen gas (O2) and 3.4 moles of carbon monoxide (CO)  entered the reaction

Explanation:

The rule of three or is a way of solving problems of proportionality between three known values and an unknown value, establishing a relationship of proportionality between all of them. That is, what is intended with it is to find the fourth term of a proportion knowing the other three. Remember that proportionality is a constant relationship or ratio between different magnitudes.

If the relationship between the magnitudes is direct, that is, when one magnitude increases, so does the other (or when one magnitude decreases, so does the other) , the direct rule of three must be applied. To solve a direct rule of three, the following formula must be followed:

a ⇒ b

c ⇒ x

So

In this case, it is possible to use the reaction stoichiometry of the reaction (that is, the relationship between the amount of reagents and products in a chemical reaction) and the rule of three to calculate the quantities of moles requested:

moles of O₂=1.7 moles

moles of CO=3.4

If 3.4 moles of carbon dioxide (CO2) form at the end of the reaction, 1.7 moles of oxygen gas (O2) and 3.4 moles of carbon monoxide (CO)  entered the reaction

answer : one can design an experiment using a liquid and an additive that can be added to the liquid and observe the chemical changes in the reaction species.

one would need a beaker which is filled with a known amount of the liquid in which thermometer is placed to measure the temperature changes; after addition of the additive to the liquid solution one can note down the temperature change and find whether the reaction is endothermic or exothermic in nature. by subtracting the initial temperature value with the final temperature one can find the temperature changes.

various combinations of liquid and additive can be used. liquid in this case can be a known quantity of water and additives can be epsom salt or without epsom salt the experiment can be conducted to notice the changes. water and ice, hydrogen peroxide and dry yeast, vinegar and baking soda,etc.