AccelePrep for the ACT Test 2nd Edition Student Text

198 • S URGE TO S UCCESS ! S CIENCE T EST P REP

ANALYSIS

Analysis items go a bit deeper than comprehension items. Analysis items frequently require the following skills: • Identify trends or otherwise explain the data that are presented. • Draw a conclusion or formulate a hypothesis based on the data of an experiment. • Evaluate the method used in an experiment. • Interpolate or extrapolate data from an experiment. • Predict the results of an additional experimental trial under different conditions. • Analyze what would support or refute an argument. According to the kinetic molecular theory of gases, all gases consist of particles (atoms or molecules) in continuous, random motion. In an ideal gas, particles move freely without interacting with one another except for brief elastic collisions. Particles of a gas at a particular temperature will have a range of different speeds. The distribution of particle speeds, that is, the number of particles moving with a certain speed, is given by the Maxwell-Boltzmann distribution curves. The most probable speed for the particles is represented by the peak of the curve. For a given distribution, the area under the curve corresponds to the total number of particles of a gas sample. To illustrate how mass affects molecular speed, Figure 1 gives the Maxwell-Boltzmann distributions for the common gases in Table 1 ƒ– ƒ ϐ‹š‡† –‡’‡”ƒ–—”‡ ȋ͵ͲͲ ȌǤ ‘ ‹ŽŽ—•–”ƒ–‡ Š‘™ –‡’‡”ƒ–—”‡ ƒˆˆ‡…–• molecular speed, Figure 2 gives the Maxwell-Boltzmann distributions for nitrogen gas (N 2 ) at several temperatures. Table 1: Molar Mass of Common Gases (grams/mole) H 2 (hydrogen) 2.02 He (helium) 4.00 N 2 (nitrogen) 28.01 O 2 (oxygen) ͵ʹǤͲͲ Cl 2 (chlorine) 70.91 ” ȋ”›’–‘Ȍ ͺ͵ǤͺͲ

POWER TIP Pay particular attention to direct (factors change in the same direction) and inverse (factors change in opposite directions) relationships.

Examples: