How are chemical changes different from physical changes?(1 point)
Responses
They are reversible.
They are reversible.
They form new substances.
They form new substances.
They include shifts in the phase of matter.
They include shifts in the phase of matter.
They involve heat.
They involve heat.
Chemical changes are different from physical changes in several ways. Here are the main differences:
1. Reversibility: Physical changes are usually reversible, meaning you can generally change a substance back to its original form. For example, if you melt an ice cube, you can refreeze it to turn it back into a solid. In contrast, chemical changes are generally irreversible. Once a chemical change occurs, it is challenging or impossible to reverse it.
2. Formation of new substances: A chemical change involves the formation of new substances with different properties from the original substances. This occurs through a rearrangement of atoms or molecules at the molecular level. For example, when hydrogen combines with oxygen to form water, the chemical properties of the resulting water molecules are different from those of the hydrogen and oxygen molecules.
3. Shifts in the phase of matter: Physical changes involve changes in the state, or phase, of matter without altering the chemical composition of the substance. Examples include changes in temperature, pressure, or other conditions that cause a substance to change from a solid to a liquid or gas, or vice versa. In contrast, chemical changes involve a transformation of the substance at the atomic or molecular level.
4. Involvement of heat: Both physical and chemical changes can involve heat, but the heat effects are different. In physical changes, heat is often absorbed or released as a substance undergoes a change in state. For example, when ice melts, it absorbs heat energy from the surroundings. In chemical changes, heat is often released or absorbed as a result of the chemical reaction taking place. This heat, known as a thermochemical reaction, is an important factor in determining the overall energy change during a chemical reaction.
Chemical changes are different from physical changes in several ways:
1. They form new substances: In a chemical change, there is a rearrangement of atoms and bonds, leading to the formation of new substances with different chemical properties. This means that the original substances are transformed into something entirely different.
2. They are irreversible: Unlike physical changes, which can usually be reversed, chemical changes are typically permanent. Once a chemical reaction occurs, it is not easy to revert the substances back to their original form.
3. They include shifts in the phase of matter: Although physical changes can also involve changes in the state of matter, such as melting or boiling, chemical changes can occur regardless of the phase of matter. It means that a chemical reaction can take place in solids, liquids, or gases.
4. They involve heat: Chemical reactions often involve the absorption or release of heat. This is because breaking or forming chemical bonds requires energy. The heat energy can be released or absorbed during a chemical change, leading to temperature changes in the surroundings.