The main system to communicate with computers is the use of natural language in text form. To add naturalness and intelligibility, the speech form is becoming an important method to communicate with computers and other machines.Human-machine and human-robot dialogues in the next generation will be conquered by natural speech, which is fully impulsive and thus obsessed by emotion. Emotion adds expressiveness to the natural language speech. There is a great zeal to research in this field. In this paper we have proposed an algorithm for word based emotion conversion of neutral speech into emotional speech like 'happy' and 'sad' for Hindi language. This emotion conversion algorithm is based on the segmentation of the spoken utterance into words and the pitch differences of these words between different emotions. The segmentation of words in the spoken utterance is done using another algorithm of word boundary detection, which gives details of start of the word, end of the word and the no. of words in a sentence. This algorithm of word boundary detection is devised for Hindi language and is based on two main prosodic features 'pitch' and 'intensity'.