Chemical and physical changes
How to identify a chemical change
Chemical reactions
Chemical equations
Conservation of mass
100
Is cutting a paper a physical or a chemical change?
It's a physical change.
100
What change can you appreciate when an apple is rotting?
You can appreciate that the color is changing from yellow to brown.
100
Decide which are the reactants and which are the products in the following reaction: Hydrogen reacts with nitrogen to produce ammonia.
The reactants are hydrogen and nitrogen and the product is ammonia.
100
True or false: The formulas of the reactants appear after the arrow.
False: The formulas of the reactants appear before the arrow.
100
Who proposed the law of conservation of mass?
Lavoisier.
200
Is melting water a physical or a chemical change?
It's a physical change.
200
What change can you appreciate when an egg is rotting?
You can appreciate a new smell (it smells like sulfur).
200
Decide which are the reactants and which are the products in the following reaction: Lithium reacts with water to produce hydrogen and lithium hydroxide.
Reactants: Lithium and water. Products: Hydrogen and lithium hydroxide.
200
What do we use to separate the formula of one reactant from the formula of other reactant?
The formulas are separated with a plus sign.
200
46 g of sodium react with bromine to produce 206 g of sodium bromide. How much bromine has reacted?
160 g
300
Is mixing vinegar and bicarbonate a physical or a chemical change?
It's a chemical change
300
What change can you appreciate when you are burning paper?
You can see that the paper is being transformed into smoke and ashes.
300
What is the difference between a chemical reaction and a chemical equation?
A chemical equation is the representation of a chemical reaction.
300
Write the chemical equation of the following chemical reaction: One molecule of sodium hydroxide reacts with one molecule of hydrogen chloride to produce one molecule of sodium chloride and one molecule of water.
NaOH + HCl --> NaCl + H2O
300
46 g of sodium react with 73 g of hydrogen chloride to produce 117 g of sodium chloride and hydrogen. How much hydrogen has been produced?
2 g
400
Is mixing salt and water a physical or a chemical change?
It's a physical change
400
What change can you appreciate when you are decomposing water with an electrical current?
You can see bubbles of hydrogen and oxygen.
400
What is a chemical reaction?
A chemical reaction is a process in which one or more substances, the reactants, are converted to one or more different substances, the products.
400
Read the following chemcial equation: CH4 + 2 O2 --> CO2 + 2 H2O
One molecule of methane reacts with two molecules of oxygen to produce one molecule of carbon dioxide and two molecules of water.
400
Fill-in the blanks: According to the law of conservation of mass, chemical reactions do not _________ or ________ matter, they only _____________ matter. Therefore, the mass of the _____________ is equal to the mass of the ____________
According to the law of conservation of mass, chemical reactions do not create or destroy matter, they only transform matter. Therefore, the mass of the reactants is equal to the mass of the products.
500
What is the main difference between a physical and a chemical change?
Physical changes do not produce new substances while chemical changes produce new substances.
500
Name six indicators of chemical changes.
1. Production of an odor. 2. Change in color. 3. Change in temperature. 4. Emission of gases. 5. Formation of a solid. 6. Production of light.
500
Why are new substances formed in a chemical reaction?
Because the atoms which form the reactants reorder and join in a different way.
500
Read the following chemical equation: 2 Li + Cl2 --> 2 LiCl
Two atoms of lithium react with one molecule of chlorine to produce two molecules of lithium chloride.
500
Why is mass conserved in chemical reactions?
When a chemical reaction is taking place, the atoms which form the reactants reorder and join in a different way but they do not change their mass when they reorder.
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