Reactions and phase transitions

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• Leerjaar 3

H4 Chemical reactions

H3 Chemical reactions

• Periodic tabel
• Reactions and phase transitions
• Reaction equations
• decomposition reactions
• Combustion reactions
• Reagents

Program of today

• Quizlet elements of the periodic table 
• Reactions
• Phase transitions
• Chemical reactions in words
• Law of conservation of mass

Reactions

Chemical reaction: process in which molecules change composition.

• The molecules in a substance change

 

Phase transitions

Phase transitions: the atoms in a molecule do not change composition, but the distance between the molecules does.

Reaction diagram:

Water (l) -> water (g)

What changes in a chemical reaction?

1. Nothing changes
2. The distance between the molecules
3. How hard the molecules vibrate
4. The composition of the atoms in the molecules

What changes in a phase transition?

1. Nothing changes
2. The distance between the molecules
3. How hard the molecules vibrate
4. The composition of the atoms in the molecules

Chemical reactions in words

In a chemical reaction, the reactants disappear and new substances are created with new properties and a new substance name; the reaction products.

Vraag: is een fase-overgang wel of geen reactie?

Reaction diagrams

A schematic representation of a chemical reaction or phase transition.

Water (g) -> water (l)

Water (l) -> waterstof (g) + zuurstof (g)

Is the following reaction diagram a...
methane (g) + oxygen (g) -> carbon dioxide (g) + water (l)

1. Chemical reaction
2. phase transition

Is the following reaction diagram a...
sugar (s) -> sugar (aq)

1. Chemical reaction
2. phase transition

Is the following reaction diagram a...
sodium sulfate (s) -> sodium oxide (s) + sulfur trioxide (g)

1. Chemical reaction
2. phase transition

Signal words

• reacts with => substances that must react stand in front of the arrow!
• formed from=> substances that are formed stand behind the arrow!
• arise from => substances that are formed stand behind the arrow!
• made out of  => substances that are formed stand behind the arrow!

Example

If you strongly heat the solid sodium sulfate, the solid sodium oxide and the gas sulfur trioxide are formed.

Example

If you strongly heat the solid sodium sulfate, the solid sodium oxide and the gas sulfur trioxide are formed.

sodium sulfate (s) -> sodium oxide (s) + sulfur trioxide (g)

Which reaction equation belongs to this reaction: Water is formed from hydrogen and oxygen.

1. water (l) -> oxygen (g) + hydrogen (g)
2. oxygen (g) + hydrogen (g) -> water (l)

Which reaction equation belongs to this reaction: Ammonia gas can be made from the gases nitrogen and hydrogen.

1. nitrogen (g) + hydrogen (g) -> ammonia (g)
2. ammonia (g) -> nitrogen (g) + hydrogen (g)

Reagents

A reagent (plural reagents) is a substance used to demonstrate the presence of a particular substance.

• Selective
• Sensitive

Law of conservation of mass

For any chemical process in a closed system, the total mass of the reactants remains equal to the total mass of the reaction products.

• No atoms are created or destroyed in chemical reactions.

Summary

• In a chemical reaction, the molecules in a substance change
• during a phase transition, the molecules do not change, but the distance between the molecules.
  
• with signal words you can reason whether a substance is before or after the arrow.
  
• The mass of the products before the arrow must always be the same as the mass of the products after the arrow (law of conservation of mass)

Homework

• Make the exercises of section  2 till 80% and exercise 1 of section 3
•  done? read section 3 and make the exercises