Two chemistry students are preparing for the “Getting the Volume Right” lab challenge. Their goal is to fill a 1000-mL graduated cylinder with CO2 gas
from a chemical reaction. They will react Na2CO3 with an excess of HCl acid to
generate the gas. If the temperature on the day of the contest is 19.4oC and
the room pressure is 1007 mbar, how many grams of Na2CO3 must they add
to the acid to produce the desired volume of CO2 gas? How many moles of
HCl will they need?

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answer; protein;

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.