Sodium salt of caboxylic acid that is sodium actetate (CH3COONa) when heated with soda lime (NaOH - sodium hydroxide).A decaoboxylation reaction takes place that is carbon dioxide is removed or eliminated from CH3COONa so to give product methane (CH4 ) and sodium carbonate ( Na2CO3 ), the equation for this reaction is :
CH3COONa + NaOH ---------> CH4 + Na2CO3