STEMA FAIR MANUAL 2015

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Gas law equation

1. A gas occupies 12.3 liters at a pressure of 40.0 mm Hg. What is the volume when the pressure is increased to 60.0 mm Hg?
2. If a gas at 25.0 °C occupies 3.60 liters at a pressure of 1.00 atm, what will be its volume at a pressure of 2.50 atm?
3. To what pressure must a gas be compressed in order to get into a 3.00 cubic foot tank the entire weight of a gas that occupies 400.0 cu. ft. at standard pressure?
4. A gas occupies 1.56 L at 1.00 atm. What will be the volume of this gas if the pressure becomes 3.00 atm?
5. A gas occupies 11.2 liters at 0.860 atm. What is the pressure if the volume becomes 15.0 L?
6. 500.0 mL of a gas is collected at 745.0 mm Hg. What will the volume be at standard pressure?
7. Convert 350.0 mL at 740.0 mm of Hg to its new volume at standard pressure.
8. Convert 338 L at 63.0 atm to its new volume at standard pressure.
9. Convert 273.15 mL at 166.0 mm of Hg to its new volume at standard pressure.
10. Convert 77.0 L at 18.0 mm of Hg to its new volume at standard pressure.
11. When the pressure on a gas increases, will the volume increase or decrease?
12. If the pressure on a gas is decreased by one-half, how large will the volume change be?
13. A gas occupies 4.31 liters at a pressure of 0.755 atm. Determine the volume if the pressure is increased to 1.25 atm.
14. 600.0 mL of a gas is at a pressure of 8.00 atm. What is the volume of the gas at 2.00 atm?
15. 400.0 mL of a gas are under a pressure of 800.0 torr. What would the volume of the gas be at a pressure of 1000.0 torr?
16. 4.00 L of a gas are under a pressure of 6.00 atm. What is the volume of the gas at 2.00 atm?
17. A gas occupies 25.3 mL at a pressure of 790.5 mm Hg. Determine the volume if the pressure is reduced to 0.804 atm.
18. A sample of gas has a volume of 12.0 L and a pressure of 1.00 atm. If the pressure of gas is increased to 2.00 atm, what is the new volume of the gas?
19. A container of oxygen has a volume of 30.0 mL and a pressure of 4.00 atm. If the pressure of the oxygen gas is reduced to 2.00 atm and the temperature is kept constant, what is the new volume of the oxygen gas?
20. A tank of nitrogen has a volume of 14.0 L and a pressure of 760.0 mm Hg. Find the volume of the nitrogen when its pressure is changed to 400.0 mm Hg while the temperature is held constant.

Other Evidence for Evolution

Modern-day organisms can provide clues about evolution. By
comparing organisms, scientists can infer how closely related the
organisms are in an evolutionary sense. Scientists compare body
structures, development before birth, and DNA sequences to
determine the evolutionary relationships among organisms.
An organism’s body structure is its basic body plan, such as how its bones
are arranged. Fishes, amphibians, reptiles, birds, and mammals, for example,
all have a similar body structure—an internal skeleton with a backbone. This
is why scientists classify all five groups of animals together as vertebrates.
Presumably, these groups all inherited these similarities in structure from an
early vertebrate ancestor that they shared. Similar structures that related
species have inherited from a common ancestor are called homologous
structures. Sometimes scientists find fossil evidence that supports the
evidence provided by homologous structures. For example, fossils show that
the ancestors of today’s whales had legs and walked on land. This supports
other evidence that whales and humans share a common ancestor.
Scientists can also make inferences about evolutionary relationships
by comparing the early development of different organisms. For
example, an adult turtle, a chicken, and a rat look quite different. But
during early development these three organisms go through similar
stages. These similarities suggest that these three vertebrate species are
related and share a common ancestor.
Scientists infer that species with similar body structures and
development patterns inherited many of the same genes from a common
ancestor. Recall that genes are made of DNA. By comparing the sequence
of nitrogen bases in the DNA of different species, scientists can infer how
closely related the species are. The more similar the sequences, the more
closely related the species are. Recall also that the DNA bases along a gene
specify what type of protein will be produced. Thus, scientists can also
compare the order of amino acids in a protein to see how closely related
two species are. Recently, scientists have developed techniques that allow
them to extract, or remove, DNA from fossils. The DNA from fossils has
provided new evidence about evolution.
Scientists have combined evidence from fossils, body structures, early
development, and DNA and protein sequences to determine the
evolutionary relationships among species. In most cases, DNA and
protein sequences have confirmed conclusions based on earlier evidence.
Scientists use such combined evidence to construct branching trees. A
branching tree is a diagram that shows how scientists think different
groups of organisms are related.

Biology/Evolution/The Fossil record

The Fossil Record

Some of the most important clues to Earth’s past are fossils. A fossil is

the preserved remains or traces of an organism that lived in the past.

Most fossils form when organisms that die become buried in

sediments. Sediments are particles of soil and rock. Layers of sediments

build up and cover the dead organism. Over millions of years, the layers

harden to become sedimentary rock. Some remains that become buried

in sediments are actually changed to rock. These fossils are called

petrified fossils. Sometimes shells or other hard parts buried by

sediments are gradually dissolved. A hollow space in sediment in the

shape of an organism or part of an organism is called a mold. Sometimes

a mold becomes filled in with hardened minerals, forming a cast.

Organisms can also be preserved in ice, tar, or amber.

Scientists can determine a fossil’s age in two ways: relative dating and

absolute dating. Scientists use relative dating to determine which of two

fossils is older. In a sequence of rock layers, the layers at the top are younger

than the lower layers. Therefore, fossils found in top layers are younger than

fossils found in bottom layers. Another technique, called absolute dating,

allows scientists to determine the actual age of fossils. The rocks that fossils

are found near contain radioactive elements, unstable elements that decay,

or break down, into different elements. The half-life of a radioactive element

is the time it takes for half of the atoms in a sample to decay. Scientists can

compare the amount of a radioactive element in a sample to the amount of

the element into which it breaks down to calculate the age of the rock.

The millions of fossils that scientists have collected are called the fossil

record. Despite gaps in the fossil record, it has given scientists a lot of

important information about past life on Earth. Almost all of the species

preserved as fossils are now extinct. A species is extinct if no members of

that species are still alive. Scientists have calculated the ages of many

different fossils and rocks. From this information, they have created a

“calendar” of Earth’s history called the Geologic Time Scale that spans more

than 4.6 billion years. The largest length of time in the scale is Precambrian

Time. After the Precambrian, the scale is divided into three major blocks

called the Paleozoic Era, the Mesozoic Era, and the Cenozoic Era.

According to one theory, called gradualism, evolution occurs slowly

but steadily. Tiny changes in a species gradually add up to major changes

over very long periods of time. According to another theory, called

punctuated equilibria, species evolve during short periods of rapid

change. Species evolve quickly when groups become isolated and adapt

to new environments. Most scientists think that evolution can occur gradually at some times and fairly rapidly at others.

Biology/Evolution/Darwin

I n 1831, Charles Darwin left England on board the HMS Beagle. On

the ship’s voyage, Darwin was amazed by the tremendous diversity, or

variety, of living things he saw. Today, scientists have identified more

than 1.7 million species of organisms. A species is a group of similar

organisms that can mate with each other and produce fertile offspring.

In 1835, the Beagle reached the Galapagos Islands in the Pacific Ocean.

Darwin was surprised that many of the plants and animals on the

Galapagos Islands were similar to organisms on mainland South America. However, there were also important differences. Darwin inferred that a small number of different species had come to the islands from the mainland.

Eventually, their offspring became different from the mainland relatives. The finches on the Galapagos Islands were noticeably different from one island to another. The most obvious differences were the varied sizes and shapes of the birds’ beaks. Beak shape is an example of an adaptation, a trait that helps an organism survive and reproduce. Darwin reasoned that plants and animals on the islands faced conditions that were different from those on the mainland. Perhaps, Darwin thought, the species gradually changed over many generations and became better adapted to the new conditions.The gradual change in a species over time is called evolution. Darwin’s ideas are often referred to as the theory of evolution. A scientific theory is a welltested

concept that explains a wide range of observations. In his book The Origin of Species, Darwin explained that evolution

occurs by means of natural selection. Natural selection is the process by

which individuals that are better adapted to their environment are more

likely to survive and reproduce than other members of the same species.

A number of factors affect the process of natural selection:

overproduction, competition, and variations. Any difference between

individuals of the same species is called a variation. Some variations

make certain individuals better adapted to their environment because of

helpful traits they possess. Over a long period of time, natural selection

can lead to evolution. Helpful variations gradually accumulate in a

species, while unfavorable ones disappear. Without variations, all

members of a species would have the same traits. Only traits that are

inherited, or controlled by genes, can be acted upon by natural selection.

Isolation, or complete separation, occurs when some members of a

species become cut off from the rest of the species. A new species can

form when a group of individuals remains separated from the rest of

its species long enough to evolve different traits. Geographic isolation

has occurred in the past because of continental drift.