Examples of substance in the following topics:
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- Substances are composed of pure elements or chemically bonded elements, whereas mixtures are composed of non-bonded substances.
- All compounds are substances, but not all substances are compounds.
- Simple or seemingly pure substances found in nature can in fact be mixtures of chemical substances.
- A mixture refers to the physical combination of two or more substances in which the identities of the individual substances are retained.
- Introduction to classifying matter as a substance or a mixture of substances.
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- The molar mass of a particular substance is the mass of one mole of that substance.
- Even the smallest quantity of a substance will contain billions of atoms, so chemists generally use the mole as the unit for the amount of substance.
- In other words, a mole is the amount of substance that contains as many entities (atoms, or other particles) as there are atoms in 12 grams of pure carbon-12.
- Each ion, or atom, has a particular mass; similarly, each mole of a given pure substance also has a definite mass.
- Molar mass is the mass of a given substance divided by the amount of that substance, measured in g/mol.
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- Another way to think about this is that a physical change does not cause a substance to become a fundamentally different substance but a chemical change causes a substance to change into something chemically new.
- For example, mixing salt and pepper creates a new substance without changing the chemical makeup of either component.
- Phase changes are changes that occur when substances are melted, frozen, boiled, condensed, sublimated, or deposited.
- They are also physical changes because they do not change the nature of the substance.
- A chemical change might also result in the formation of a precipitate, such as the appearance of a cloudy material when dissolved substances are mixed.
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- Substances that exist in the gas phase exhibit negligible intermolecular forces.
- Near absolute zero, a substance exists as a solid.
- The temperature of a substance is a measure of the average kinetic energy of the particles.
- Under standard conditions (1 atm, 273 K), a substance which exists as a gas is called a pure gas and (disregarding any substance-specific intermolecular forces or particle volume that could alter this value) has a volume of 22.4 L per mole.
- At STP, if the boiling point of a given substance is below 273 K then you would expect that substance to be in gas form.
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- Heat capacity is a measure of the amount of heat energy required to change the temperature of a pure substance by a given amount.
- the molar heat capacity, which is the heat capacity per mole of a pure substance.
- the specific heat capacity, often simply called specific heat, which is the heat capacity per unit mass of a pure substance.
- It discusses how the amount of heat needed for a temperature change is dependent on mass and the substance involved, and that relationship is represented by the specific heat capacity of the substance, C.
- Calculate the change in temperature of a substance given its heat capacity and the energy used to heat it
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- Solubility often depends on temperature; the solubility of many substances increases with increasing temperature.
- During recrystallization, an impure substance is taken up in a volume of solvent at a temperature at which it is insoluble, which is then heated until it becomes soluble.
- The impurities dissolve as well, but when the solution is cooled, it is often possible to selectively crystallize, or precipitate, the desired substance in a purer form.
- This chart shows the solubility of various substances in water at a variety of temperatures (in degrees Celsius).
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- They also need a way to compare these numbers and relate them to the weights of the substances, which they can measure and observe.
- Avogadro's number is defined as the number of elementary particles (molecules, atoms, compounds, etc.) per mole of a substance.
- It is defined as the amount of a substance that contains as many particles as there are atoms in 12 grams of pure carbon-12.
- So, 1 mol contains 6.022×1023 elementary entities of the substance.
- Another property of Avogadro's number is that the mass of one mole of a substance is equal to that substance's molecular weight.
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- To accomplish this, combine the standard enthalpy and the standard entropy of a substance to get the standard free energy of a reaction:
- Recall that the symbol ° refers to the standard state of a substance measured under the conditions of 1 atm pressure or an effective concentration of 1 Molar and a temperature of 298K.
- As with standard heats of formation, the standard free energy of a substance represents the free energy change associated with the formation of the substance from the elements in their most stable forms as they exist under the standard conditions of 1 atm pressure and 298K.
- Most tables of thermodynamic values list ΔGf°'s for common substances.
- *Remember that substances in elemental form (such as O2) have $\Delta G^o_f$ values equal to zero.
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- As introduced in the previous concept, the mole can be used to relate masses of substances to the quantity of atoms therein.
- This is an easy way of determining how much of one substance can react with a given amount of another substance.
- From moles of a substance, one can also find the number of atoms in a sample and vice versa.
- Therefore, given the relationship 1 mol = 6.022 x 1023 atoms, converting between moles and atoms of a substance becomes a simple dimensional analysis problem.
- Convert between the number of moles and the number of atoms in a given substance using Avagadro's number
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- For example, the freezing point of a substance is a physical property: when water freezes, it's still water (H2O)—it's just in a different physical state.
- Chemical properties cannot be determined just by viewing or touching the substance; the substance's internal structure must be affected for its chemical properties to be investigated.
- Physical properties are properties that can be measured or observed without changing the chemical nature of the substance.
- Chemical stability refers to whether a compound will react with water or air (chemically stable substances will not react).