aufreißen
to tear open
To open something quickly with force and energy, often in a way that damages it.
Er hat den Briefumschlag ungeduldig aufgerissen.
He impatiently tore open the envelope.

to tear open
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to tear open
To open something quickly with force and energy, often in a way that damages it.
Er hat den Briefumschlag ungeduldig aufgerissen.
He impatiently tore open the envelope.

'Aufreißen' (to tear open) is a separable verb. The prefix 'auf-' comes at the end in main clauses. In subordinate clauses and in the infinitive with 'zu', the verb stays together.
Er reißt das Fenster mit einem Ruck auf.
He tears the window open with one sudden pull.
The verb consists of the prefix 'auf' (which often means 'open') and 'reißen' (to tear). The literal meaning of 'aufreißen' (to tear open) helps you understand many uses where something is opened quickly or suddenly.
Die alte Wunde ist beim Sport wieder aufgerissen.
The old wound split open again during sports.
In the meaning 'to open with force', the verb is often used with objects such as 'einen Brief' (a letter), 'eine Packung' (a package), or 'ein Geschenk' (a present).
Die Kinder rissen ihre Geschenke ungeduldig auf.
The children impatiently tore open their presents.
When skin, a wound, or the ground 'aufreißt' (splits open), the verb is used without an object, i.e. intransitively. The subject is the thing that develops cracks by itself.
Durch die Trockenheit ist der Erdboden aufgerissen.
Because of the dryness, the ground has split open.
As a reaction to surprise or shock, 'aufreißen' (to open wide) is almost always used in the fixed expressions 'die Augen aufreißen' (to open one's eyes wide) or 'den Mund aufreißen' (to open one's mouth wide).
Er riss den Mund auf, als er den Preis hörte.
He opened his mouth wide when he heard the price.
The meaning 'to approach someone in order to start a relationship' is very colloquial. In this use, the verb always needs an accusative object.
Er hat versucht, sie auf der Party aufzureißen.
He tried to pick her up at the party.
to open
'öffnen' and 'aufreißen' can both mean that something closed is opened. 'öffnen' is neutral and works with many things, for example a door, a window, or a bottle. 'aufreißen' sounds much stronger: you open something quickly, with force, and often carelessly. Something may get damaged in the process. With eyes or a mouth, 'aufreißen' means opening them wide in surprise or shock. In everyday language, 'öffnen' is the normal choice when no special force or excitement is meant.

Vor Hunger riss Max die Packung Kekse auf.
Max was so hungry that he tore open the package of cookies.
Kannst du bitte das Fenster öffnen, damit frische Luft hereinkommt?
Can you please open the window so that fresh air can come in?