The total pressure of a mixture of three gases in container is 3,345 mmhg. gas #1 has a pressure of 988 mmhg and gas #2 has a pressure of 1289 mmhg. what is the pressure of gas #3?

According to Dalton's law of partial pressure: The pressure exerted by a mixture of gases is sum partial pressure of each gas exert on the container.

Here we have mixture of three gases so the total pressure of three gases will be sum of their individual or partial pressures

Therefore the partial pressure of third gas will be

The pressure of gas#3 is 1068mmHg

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.

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