Unbelief is it the opposite of faith?

“For it is with your heart that you believe and are justified, and it is with your mouth that you profess your faith and are saved.” Romans 10:10

But the things that come out of a person’s mouth come from the heart, and these defile them.

Jesus said to him, “If  you can believe, all things are possible to him who believes.  Immediately the father of the child cried out and said with tears, “Lord, I believe; help my unbelief!”

Lord, create in me a clean heart so that my words will glorify You. Help my unbelief, Lord. I pray this in Jesus name.