how do you know if a reaction is endothermic?

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for example look at this question. How can you tell which ones are endothermic?

[oneoneoneone]

You need to heat something for it to sublime so the first one is endothermic.
I'm not entirely sure about this one but often direct full redox reactions are exothermic so it follows that the reverse of one would be endothermic.
Burning carbon is exothermic so reducing CO2 would be endothermic.
Since it takes energy to remove an electron from an atom, it follows that it woudl release energy when a cation accepts an electron, so this is exothermic.