Passage VI
The ideal gas law (IGL) describes the physical behavior of gases. Although ideal gases do not exist, the IGL is a useful model for many real gases. A researcher used the IGL to predict trends in the pressure of an ideal gas under various sets of conditions. Then, the researcher performed 3 experiments to compare the IGL predictions with trends in the pressure of each of 2 real gases (Gas Y and Gas Z) under the same sets of conditions. The conditions that were varied for an ideal gas, for Gas Y, and for Gas Z were the following:
·The gas temperature, T (in kelvins, K)
·The amount of gas, n (in moles, mol; 1 mol=6.0 x 1023 atoms or molecules), in a container
·The volume of the container, V (in liters, L)
Experiment 1
The pressure, P (in megapascals, MPa), of an n=1 mol sample of Gas Y in a 1.0 L container was recorded for values of T from 200 K to 450 K. This procedure was repeated for Gas Z. Figure 1 shows the trends for the 2 gases. Also shown is the trend predicted by the IGL.
Experiment 2
The pressure, P, of a sample of Gas Y in a 1.0 L container was recorded for values of n from 1 mol to 10 mol, while T was held constant at 400 K. This procedure was repeated for Gas Z. Figure 2 shows the trends for the 2 gases and the trend predicted by the IGL.
Experiment 3
The pressure, P, of an n=1 mol sample of Gas Y in a container of adjustable volume was recorded for values of V from 0.5 L to 1.0 L. while T was held constant at 400 K. This procedure was repeated for Gas Z. Figure 3 shows the trends for the 2 gases and the trend predicted by the IGL.
34. In which experiments was T held constant?
Your Answer is
Correct Answer is H
Explanation
Comparing the three charts, it can be seen that only in figure 1 corresponding to Experiment 1, the independent variable represented by the abscissa is T;
T is neither an independent variable nor a cause in the last two charts variable, so T in Experiments 2 & 3 is a constant