Chemistry Problem Solving, Chemistry Problem Solving

1. Melting, dissolving, crystal precipitation, evaporation (volatilization), etc. are all physical changes. It is related to its physical properties: melting point, solubility, volatility, etc. It has nothing to do with chemical properties.

2. For example, the combustion of C in oxygen is an exothermic reaction. At the same time, a new substance, an oxide of C, is formed. A change in temperature is a physical change, and a new substance is generated into a chemical change.

However, for example, when boiling water, the water changes from a liquid state to a gaseous state, which is a physical change, but its essence of the water molecule does not change, and it is not a chemical change.

3. Nuclear fission is to directly change the composition of atoms, although new substances are generated, but it does not meet the law of conservation of elements in chemical reactions. Moreover, nuclear fission only removes one or a few neutrons to form new atoms, not a chemical reaction to obtain new matter. So chemistry is the science of synthesizing new molecules, but it is not the science of synthesizing new atoms.

Because new atoms cannot be obtained by chemical reactions.

The physical change is that no new products are generated, and the items in 1 are only changes in their respective states, but the chemical properties do not change, for example, the evaporation of water is a physical change. Chemical changes are accompanied by the formation of new construction and the reduction of fractures.

2 There must be physical changes in chemical changes because molecules and atoms participate in the reaction in chemical reactions, so chemical substances are cleaved into molecules and atoms from the state that we can see with the naked eye, and physical changes occur in them. That is, this process can be seen from the change in energy when dissolved.

And there is not necessarily a chemical change in the physical change, which is easy to understand, but it is only a change in the physical state of the substance, and it does not have to be a chemical change. A piece of diamond can be crushed under vacuum, but this is only a change in shape. This example is more extreme.

1 That's not a chemical change, it's a change in the intermolecular forces, so the state changes. Metallic bonds, ionic bonds are not chemical bonds 2 Physical change must have no chemical change, otherwise it is a chemical change. Chemical changes have temperature changes, i.e., physical changes 3 Chemistry is that changes are macroscopic, and nuclear fission is produced by the collision of physical particles.

1.The essence of a chemical reaction is the breaking of old bonds and the formation of new ones. Fracture and formation must be satisfied at the same time, and the example you gave does not. For example, sodium chloride is dissolved in water and has ionic bond breakage, but no new bond is formed.

The dipole moment of the molecule = the sum of the dipole moments of all covalent bonds The dipole moment is a vector quantity, so the sum is not a simple addition, but a vector sum, that is, the direction and magnitude are taken into account. The direction of the dipole moment in chemistry is specified as the center of positive charge pointing towards the center of negative charge. That is, for a covalent bond, the dipole moment direction is the direction of the electronegative small atom towards the electronegative atom with the large electronegativity.

After determining the magnitude and direction of the dipole moment for each covalent bond, the dipole moment of the entire molecule can be obtained by vector addition. If the result is zero, it means that the molecule is non-polar, otherwise it is polar. Normally, a molecule is non-polar if there are no polar covalent bonds (elemental molecules) in the molecule, or if there is special symmetry (there is a center of symmetry, three or more symmetry planes, two or more non-coincident axes of rotation, etc.).

Others are polar molecules. Hydrocarbons are particularly symmetrical except for a few (including methane.

The carbon here is over 100%.

This is called a carbonyl group, if the carbon is connected to an H, it is called an aldehyde group, if it is connected to a halogen such as Cl, it is called an acyl group, if it is connected to -OH it is called a carboxyl group, and if it is connected to -O-R it is called an ester group.

Answer: AA, no. Cl2 is more oxidizing than FeCl3, and FEI2 can be oxidized, but the product must have I2, because its oxidation is weaker than Fe3+, unless there is no Fe3+, after all I2 is generated, Fe3+ can be generated.

b, it can happen. Cl2 is more oxidizing than FeCl3, and FeCl3 is more oxidizing than I2, so in the end it must be I2 generated, not FeCl3, so it is also true.

c, it can happen. CO2O3 is the most oxidizing, it can oxidize the other three substances, and the reaction can be carried out.

d, it can happen. Fe3+ is more oxidizing than I2 and can oxidize its ions into elemental substances.

A is N4H4(SO4)2 and B is N4 (the elemental composition of A is known to be similar to (NH4)2SO4, and then the molar mass is made).

No, because N4H4(SO4)2 reacts with basic substances to form N4, which causes nitrogen loss.

cation of a, see figure. Similar to the structure of white phosphorus, because there are also lone pairs of electrons on n, it can form n h coordination bonds.

Equation 4 CSOH + 8 NH3 = 4 CSNh2 + N4 +6 H2 +4 H2O

Here's my teacher's answer, in two parts:

The first time is the problem ** :d diagram really has two health. (b) There is more than one type of diagram d; There are more than three types of C and D diagrams; D term 2+4=6 is exactly the number of h, so the number of 2 chlorine and 4 chloro substitution species is the same.

The second time: Me: How to calculate the prism, the top and the bottom are actually the same; And that d is inconsistent on the left and right sides due to the vertical in the middle? Teacher:

I'll give you a reference, I don't know if I'm sorry, after all, I haven't done it for so long.

B is benzene, each carbon atom has the same properties, it is sp2 hybridization, so there is no doubt that its monochlorinated compound is one, d and p are bridging ring compounds, where d has two carbon atoms (unsaturated carbon and saturated carbon), and the two sides of the bridge are symmetrical, so there should be two chlorinated substances; p is saturated carbon and has a symmetrical structure, so there is one chlorinated substance.

1. Let the ionized c(h+)=x, then x 2=cxka=x=10

pH=2, let the ionized c(h+)=x, then xx(x+ solution x is approximately equal to 10 ph=

For ideal gases.

If the temperature of the gas does not change, it means that you do not change.

U w q gas expands to do work externally, so it absorbs heat to keep u constant.

Entropy change heat temperature kJ 298k

So it is necessary to see if this question is the ideal gas condition).

Oops, it looks familiar, but I've forgotten how to do it now.