Why does an aerial firework require two explosions of black powder

In an exothermic reaction the bonding energy of the product is: less than the reactants same as the reactants greater than the reactants dependent upon the presence of a catalyst

Indicate whether the specified alkyl halides will form primarily substitution products, only elimination products, both substitution and elimination products, or no products when they react with sodium methoxide. 1-bromobutane 1-bromo-2-methylpropane 2-bromobutane 2-bromo-2-methylpropane

The chart shows the bid provided by four contractors to complete a job. which contractor is the most cost-effective?