The main difference between Impressionism and Expressionism is in the different prefixes "im" and "ex"! But it would be too simple if the difference consisted only of this. Impressionism and expressionism are two separate trends in art and for each of them there are specific features.

ORIGIN

Impressionism if due to the word of "to impress" — leave a mark, leave impact in memory. Already on the basis of this information, the difference of concepts is clear somewhere.
Expressionism, then, comes from the word "to express" meaning reflecting on issues.

Theoretically it seems to be clear, but how are these differences expressed in the writing of pictures? I'll try to explain the difference easily.

IMPRESSIONISM

Impressionism goes far into the 1860s, to France. The origin of the style was conducted by such famous artists as Monet, Cezanne, Manet, Renoir, Pissarro and others. In total, there were 30 members. They invented a new style for the standards of that time — to express reality as they saw it, that is, brighter, more colorful than it really was. That is, in fact, we can say that the paintings of Impressionist artists slightly overdo with colors, light and perspective, than, for example, all the usual realists.

In 1874, the above-mentioned artists prepared their works for the annual exhibition in Paris, but because of innovation, all the paintings were rejected. Then the artists organized the "Salon of the Outcast" and put their pictures straight on the street. It is not surprising that a greal deal of critics were showered on them and in one of the articles there appeared at the time the abusive title of "Impressionism".

Impressionists often painted landscapes using a brighter palette, but sometimes they sketched portraits, which often resembled ordinary moments from everyday life. Their goal was to capture not reality, but exciting moments of pleasant life through their own vision. If to compare, the pictures were somekind of streetphotographies: the plot was spontaneous.

Renoir Pierre-Auguste «Woman with an Umbrella», 1875

Claude Monet «Argenteuil», 1875

Edouart Manet «At Races», 1875

Kamil Pissarro «Hermitage at Pontoise»

Soon the liveliness of the paintings was liked even by realist artists who began to apply it in their works.

Most often impressionistic pictures cause joy, lightness, optimism. If you look closely at the technique of strokes, you can notice brave movements with a brush. The Impressionists became the first artists who did not mix paints on canvas, but pre-prepared the shades on the palette and only then they were applied to the canvas.

A group of Impressionist artists succeeded to organize 8 exhibitions during the existence of their union from 1874 to 1886. Unfortunately, the new direction was not evaluated at the proper level and the artists lived in poverty.

EXPRESSIONISM

Expressionism as a style of visual art appeared after Impressionism in 40 years in Germany before the first world war began. In their works, the artists showed a protest against the greyness and vileness of reality, portraying it in a distorted way. Accordingly, the pictures are full of depression, dissatisfaction, pessimism. They showed subjective reactions to events that occurred at that time.

Vincent Van Gogh, Edward Munch, Wassily Kandinsky and Hans Hofmann are the first Expressionist artists.

Edvard Munch «Vampire»

Emil Nolde «Joseph Recount His Dreams»

Franz Marc «Three Cats»

Wassily Kandinsky

Breaking away from reality and avoiding real and existing objects, artists preferred expressing themselves through amazing and special forms.

In the pictures of this genre, elongated figures are traced, the image is plane, primitivism is felt, but at the same time there is dynamics, colors are contrasting and, to a greater extent, gloomy. Plots of works are often based on literary subjects, at the same time, the Expressionists liked to create abstract art.

I will sum up the above: if you see a picture resembling realism, but in brighter colors, due to which the soul becomes light and pleasant feeling occurs, it means it is done in the style of impressionism; If, in front of you, there is a work that causes anxiety, sometimes incomprehensible images, is painted with vivid and dark colors, then most likely it refers to expressionism.

Photos under license CC0, if the source is not specified.

Sources: 1, 2.