during a chemical reaction the reaction mixture turns cold . Why did that happen?
Answers
CHEMICAL REACTIONS
What is a chemical reaction?
What happens to atoms and the bonds between them during a chemical reaction?
How can we identify the reactants and products of a reaction?
What examples of chemical reactions are there in indigenous practices?
we looked at the particle model of matter and specifically at changes of state. Do you remember heating and cooling candle wax to observe it melt and then solidify. The wax first changed from a solid into a liquid and then back to a solid again. These are physical changes. The chemical properties of the substance does not change.
We are now going to look at what happens when we get chemical changes in substances. These take place during chemical reactions.
How do we know a chemical reaction has taken place?
chemical reaction
reaction flask or
reaction vessel
During a chemical reaction, one or more substances are changed into new substances. Do you know of any chemical reactions? Can you mention one or two examples?
How will we know when a chemical reaction is taking place? What are the signs?
We can tell if a chemical reaction has taken place when one or more of the following things happen:
There has been a colour change inside the reaction flask.
A gas has formed. Usually we know a gas has formed when we can see bubbles. This should not be confused with boiling, which only happens when a liquid is heated to its boiling point.
A solid has formed. Usually we know that some solid material has formed when we can see a sludgy or cloudy deposit, or crystals forming.
All the signs listed above are visual, or recorded by sight. That means we can see them. Our other senses can also help us to say whether or not there was a chemical reaction:
Sometimes chemical changes can be smelled, for instance when a new material, that has a strong smell, is formed.
Other chemical changes can be felt, e.g when the reaction produces heat.
Some chemical changes can be heard, e.g. when an explosion takes place.
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