Why does warm soda go flat faster than chilled soda?
Well, a gas in water at elevated temperature is always LESS soluble than a gas at reduced temperature.
See this site. Usually, the smaller the gas molecule, the lesser its solubility. Of course, the gas in soda is carbon dioxide; in the old days when you made soft drinks (or beer) you would put a spoonful of sugar into the flat liquid when it was bottled. After sealing, the sugar would be fermented to produce small quantities of carbon dioxide gas, which would carbonate the drink.
The video below shows a demonstration of how carbon dioxide solubility is affected by temperature changes.