Factors that affect the rate of chemical reactions are
surface area of reactants (solid)
temperature
pressure
presence of catalyst
concentration
The focus here will be on the options provided in the question (starting from option d)
Adding more of a substance to a mixture has nothing to do with a chemical reaction because a mixture is a combination of two or more substances that are physically combined (NOT chemically combined) and as such, the reaction rate cannot be determined/altered.
Increasing the concentration of the reactants leads to an increase in the rate of reaction as more product will be formed as a result of this. This is so because the molecules will be able to interact better because of the increase in the number of molecules present in the reaction.
Raising the temperature of a reaction causes for effective collision which causes an increase in the rate of reaction. In chemical reactions, not all collisions leads to a reaction, the collision that causes molecules to react is what is referred to as effective collision.
Lowering the pressure of a gaseous reaction reduces the number of effective collisions and hence slows down the rate of chemical reaction. This makes option a the correct option
The thing that governs whether a reaction is exothermic is the energy given out / used up to break / form the bonds in the reaction.
<span>When two substances react, the bonds in those substances first break up, releasing energy, before re-forming in a different way, taking in energy. The nature of the bonds that are broken up and reformed determines whether more energy is given out (exothermic) or taken in (endothermic)</span>
The chemical at the heart of the air bag reaction is called sodium azide, or NaN3. CRASHES trip sensors in cars that send an electric signal to an ignitor. The heat generated causes sodium azide to decompose into sodium metal and nitrogen gas, which inflates the car's air bags.
