To investigate how reactant surface area affects the rate of a chemical reaction, students… — ACT

To investigate how reactant surface area affects the rate of a chemical reaction, students performed three trials. In each trial, $5.0\text{ g}$ of calcium carbonate ( $CaCO_3$ ) was added to $100\text{ mL}$ of $1.0\text{ M}$ hydrochloric acid ( $HCl$ ) at an initial temperature of $20.0^\circ\text{C}$ in an uninsulated beaker. The reaction is represented by the following equation:

CaCO_3(s) + 2HCl(aq) \rightarrow CaCl_2(aq) + CO_2(g) + H_2O(l) + \Delta H

The students recorded the particle size of the $CaCO_3$ , the time required for the reaction to go to completion, and the maximum temperature reached during each trial. The results are shown in the table below:

Trial	$CaCO_3$ Particle Size	Time to Completion (s)	Maximum Temperature Reached ( $^\circ\text{C}$ )
$1$	Large chunks	$240$	$21.5$
$2$	Small chips	$120$	$26.2$
$3$	Fine powder	$30$	$38.8$

Which of the following statements best explains how the maximum temperature reached acts as a confounding variable that prevents the students from drawing a valid conclusion about the effect of particle size on the reaction rate?

A
The maximum temperature reached is the independent variable, which the students should have controlled by varying the initial mass of the calcium carbonate added to each beaker.
B
The temperature differences indicate that Trial 1 was conducted in a colder room than Trial 3, showing a failure to keep the ambient experimental environment constant.
The unequal temperature rise among the trials increases the average kinetic energy of the reactants in the faster trials, meaning the difference in reaction times cannot be attributed solely to the difference in particle size.Cevap
D
The maximum temperature is a controlled variable because the reactants in all three trials began at the same initial temperature of 20.0°C.

Cevap

The correct answer explains that the unequal temperature rise among the trials increases the average kinetic energy of the reactants in the faster trials, meaning the difference in reaction times cannot be attributed solely to the difference in particle size. Since temperature is known to affect reaction rate, the fact that the temperature rose much higher in the fine powder trial than in the large chunks trial means that both temperature and surface area changed simultaneously, confounding the results.

Adım Adım Çözüm

Identify the independent, dependent, and controlled variables in the setup.

The independent variable is the particle size of calcium carbonate, and the dependent variable is the time to completion. The controlled variables include the mass of calcium carbonate, the volume and concentration of hydrochloric acid, and the initial temperature.

Establishing the variable roles is necessary to detect any extraneous variables that are not properly controlled.

Analyze the maximum temperature data across the trials.

The maximum temperature rose from

21.5^\circ\text{C}

in Trial 1 (slowest) to

38.8^\circ\text{C}

in Trial 3 (fastest).

This temperature difference shows that a variable influencing reaction rate (temperature) was not constant across trials during the reaction.

Determine how this temperature variation affects the interpretation of the results.

Higher temperatures increase the kinetic energy of reactants, which accelerates the reaction. Therefore, the faster rate in Trial 3 is caused by both the smaller particle size and the higher temperature.

This shows that temperature acts as a confounding variable, making it impossible to isolate the effect of particle size alone.

Anahtar Kavram

A confounding variable is an uncontrolled factor that varies systematically with the independent variable, making it impossible to isolate the true cause of the observed changes in the dependent variable.

Tahmini Süre:2m 0s

Soru

Cevap

Adım Adım Çözüm

Anahtar Kavram

Sık Yapılan Hatalar

Konular

Bu konudan daha fazla soru