Don't be misled by the spelling. There are quite different words. http://thefreedictionary.com/tense http://thefreedictionary.com/intense Both of your sentences make sense, but they have different meanings. It's unclear what you mean by "harder".

The words " tense" and " intense" have similar meanings. Tense can refer to a feeling state- " I am feeling tense": this means you are feeling tension, which could mean anything from feeling emotional pressure, to tension in your muscles. When something is " intense" that generally refers to a situation of great overwhelm.