To be certain that a chemical change has taken place you check the composition of the sample before and after the change. The following is a chemical property of water at 4 C is its ability to decompose into hydrogen and oxygen.
A new substance must occur.
However, there are many hints that show that a chemical might have taken place:
- a change of color
- possible release of a gas
- a precipitate
- variation of pH
- variation of temperature
- variation of viscosity
- a specific smell
The most important is the formation of new compounds.
But also:
Some indicators of a chemical reaction are:
- change of color
- change of odor
- release of a gas
- change of the temperature
- change of the viscosity
- formation of a precipitate
- change of general appearance
- possible explosion
- possible chemiluminescence
Some indicators of a chemical reaction are: - formation of new compounds - change of color
- change of odor
- release of a gas
- change of the temperature (absorption or release)
- change of the viscosity
- formation of a precipitate
- change of general appearance
- possible explosion - sometimes a sound is produced - possible chemiluminescence
Demonstrate that a release of energy occurred after the change.
The only way to be sure a chemical reaction or change has occurred is to test the composition of a sample before and after a change.
energy has been used or given out
You can tell that a new stubstance has formed
A physical change means that only the appearance of the substance has changed. So if your tear up a piece of paper, its still paper so a physical change has taken place. If you heat or freeze water its only a change of state so its still a physical change. So long as the molecular or chemical structure of the atom/substance does not change it will always be a chemical change. H20 will always be H20.
Mixing lemonade powder into water is a chemical change. This is because the powder changes the water molecules and can not be taken out.
Breaking, grinding, cracking are all examples of a physical change. The nature of the substance has not changed, just the size of the pieces has changed.
If you mean changing one element into another, like uranium 238 into plutonium 239, which happens in nuclear reactors, the word is 'transmutation'. Otherwise many chemical reactions form new substances, without the elements involved changing, and these would be called 'chemical reactions'.
Vaporization is an endothermic process; evaporation is exothermic.
Signs that a chemical change has taken place include the formation of a gas, the formation of a precipitate, a change in temperature, and a change in color.
A chemical change has taken place
The change in color indicates that a chemical reaction has taken place.
It is a chemical change. Through corrosion, a chemical reaction has taken place.
Physical change.
Fracture formation
youwill hear it
Chemical change. The formation of a precipitate is one indication that a chemical reaction has taken place.
Physical. It is a mixture of salt and water. No chemical change has taken place.
No. If you evaporate the water, the drink powder is left behind. No chemical change has taken place.
You might observe a change in color, gas bubbles being formed, a change in temperature (this might require the use of a thermometer, unless the solution actually boils), or you can test for a specific chemical by using an indicator, or analyse the solution by means of a mass spectrometer. Explosions are also a very convincing form of evidence that a chemical change has taken place.
True