Laboratory Tools and Procedures Question 1

A $\pu{0.40 g}$ sample of $\ce{Li(s)}$ is placed in an Erlenmeyer flask containing $\pu{100 mL}$ of water at $25^\degree \pu{C}$ . A balloon is placed over the mouth of the flask to collect the hydrogen gas that is generated.

Which of the following changes will most likely increase the rate of reaction between $\ce{Li(s)}$ and water?

Using

\pu{125 mL}

of water instead of

\pu{100 mL}

Using a

\pu{0.30 g}

sample of

\ce{Li(s)}

instead of a

\pu{0.40 g}

sample

Using a

\pu{0.40 g}

sample of

\ce{Li(s)}

cut into small pieces

Decreasing the water temperature before adding the

\ce{Li(s)}

Approach

By cutting the $\ce{Li(s)}$ sample into smaller pieces, we increase the rate of reaction by increasing the area of contact between $\ce{Li(s)}$ and water.

Adding additional solvent would not increase the rate of reaction since $\pu{100 mL}$ of water is more than enough to cover the small amount of $\ce{Li(s)}$ .

Reducing the amount of sample would decrease the amount of surface area in contact and thus decrease the rate of the reaction.

Typically, reactions procede faster with increasing temperatures. Faster molecular speeds cause reactants to collide and more easily overcome the activation energy.