The science that systematically studies the composition, properties, and activity of organic and inorganic substances and various elementary forms of matter.
What is Chemistry
100
A hypothesis is a provisional or working explanation, assumed true only to guide experimentation or for the sake of argument. A theory is a well established explanation.
How are theories different from hypotheses?
100
When ice melts, heat must be absorbed from the surroundings. This is because energy is required to break the hydrogen bonds that pin the water molecules in place in ice. If you stop heat from being absorbed, the ice won't melt
How does the ice in coolers stay cool?
100
Each row (or "period") on the periodic table corresponds to filling a different "shell" of electrons.
Why are first period elements unusual?
100
The reaction rate depends on the surface area of the magnesium as well as on the hydrogen ion concentration
What is the rate law for reaction of solid Mg with HCl?
200
The Baumé scale is a measure of a solution's specific gravity, not its concentration.
What is a "degree Baumé"
200
A law is just a description of a pattern in the data. A theory is an explanation for the pattern. The law shows what happens, without explanation. A theory explains how it happens, often by using using an analogy or metaphor. So whether a hypothesis that becomes well established becomes a law or a theory depends on whether it tells you what happens, or it tells you how something happens.
Do hypotheses become laws?
200
Hess's law says that reaction enthalpy doesn't depend on the route you take from the reactants to the products.
What is Hess's Law?
200
Living cells contain anywhere from 65 to 90% water by weight, so it's no surprise that most of the body's mass is oxygen
What elements are present in the human body?
200
1. The iodine clock reaction. In acidic solution
2. The iodide-catalyzed decomposition of hydrogen peroxide. This reaction produces oxygen gas
What is the mechanism of the reaction between iodide ion and hydrogen peroxide?
300
SI (or Système International d'Unités ) is the modern form of the metric system.
Is the SI the same as the metric system?
300
Apparent 'violations' of natural laws are easy to contrive if you ignore the restrictions on the data that the law is based on.
Are natural laws ever violated?
300
Breaking a chemical bond requires energy (just as stretching a spring until it breaks requires energy). Forming a chemical bond will release energy.
Why does mixing a strong acid with water release so much heat?
300
The melting points of the first period elements are extremely low, because forces between H2 molecules and between helium atoms are exceptionally weak.
Is there a trend in melting points on the periodic table?
300
Hydrolysis reactions are a large and diverse set. Here is a very simple example. Methyl halides undergo hydrolysis according to
CH3X + H2O CH3OH + H+ + X- (rate constant k1)
Why do hydrolysis reaction rates typically increase at higher pH?
400
It means that variables that can affect the data collected from an experiment are monitored and held constant.
What are controlled conditions?
400
No. A law is a description of the data.
Are laws facts?
400
When heat is lost to the air, some is absorbed by nitrogen, some is absorbed by oxygen, and a tiny amount is absorbed by argon, carbon dioxide, water vapor, and trace gases
The most helpful courses will be those that hone problem solving and critical thinking skills. The ability to communicate clearly and effectively is also important. If your high school offers a technical writing course, take it
What high school courses should I take to prepare me to be a chemistry major?
500
We presume that the same patterns will be observed anywhere in the universe. We're aware that this is a presumption, but data collected by astronomers and cosmologists so far reassure us that the physical and chemical laws that apply here apply everywhere.
Do natural laws apply everywhere?
500
Neutralization reactions are exothermic in general. But there are several conflicting processes going on in this reaction that contribute to the overall temperature change you observe.
Is heat absorbed or released when vinegar reacts with baking soda?
500
You'll find everything you need (and a lot you don't) at WebElements, the most extensive element database on the Web.
Where can I find information about elements on the Web?
500
Assertion that "a 10° temperature rise doubles reaction rates" is just a rule of thumb, not a law of nature. Like most rules of thumb, "thumbtimes it works, and thumbtimes it doesn't."
Does a 10°C temperature rise double reaction rates?