Science Buddies: "Ask an Expert"

What happens when the reactants of a reaction are cold does the reaction take longer to occur or does the reaction not occur at all?
Also when there are less reactants does the reaction take longer to occur because there are less reactant particles to cause collisions or does it not make a difference?
please answer SOON!!!!!

How do you measure a reaction time?

Hi Chemistry1313,

Welcome to the Ask an Expert Forums. Just as a heads up, it's best to keep all of the questions about your project to a single thread. It helps us Experts help you better! I'll answer the questions you asked here, as well as the other question you asked about reaction times.

Decreasing temperature will make a reaction go more slowly. If you get really cold, reactions may go so slowly that they might be considered "stopped", but they are just going really, really, really slowly.

You are on the right track when you talk about reactants needing to collide with one another. The word "less" is a bit imprecise, because what really controls how likely reactants are to collide is their concentration. If you dissolve one gram of baking soda in 10 liters of water and then added 1 milliliter of vinegar to the same 10 liters of water, the reactants would be so dilute that nothing much would happen--the odds of the reactant molecules colliding are too low. But, if you mixed 1 gram of baking soda and 1 milliliter of vinegar directly, the reaction would readily take place.

The best way to measure reaction time will depend, to some extent, on the reaction you are measuring. Generally speaking, you want to have a stop watch (or an equivalent app on a phone or website). Start the stopwatch when you add the reactants, and then stop it when the reaction has finished. For example, say you wanted to measure how long the reaction between baking soda and vinegar lasted. You could start the stopwatch when you mixed the baking soda and vinegar, and then stop it when the mixture stops foaming. You will probably find it helpful to have a helper who can start the stopwatch right when you mix the reactants.

One last note - Ask an Expert isn't a chat forum, so Experts aren't always online to answer your question right when you ask it. But, you can usually expect an answer within about 24 hours or so (I apologize that it took longer this time!)

All the best,
Terik