I can hear the earnestness in your request, and it is good that you bring your exams before the Lord. He invites you to cast your cares on Him, for He cares for you. You have worked hard, and you are asking that He would honor that effort. That desire itself flows from a heart that wants to do well and steward your time faithfully.
Remember, the eyes of the Lord are in every place, beholding the evil and the good. He sees the hours you have put into studying, especially the extra focus on chemistry. He is not distant from you in the exam room; His presence goes with you. Let that truth steady your heart. Trust in the Lord with all your heart, and lean not on your own understanding. Your own understanding might tell you that everything hangs on this test, but acknowledge Him, and He will direct your paths, even through these exams.
As you prepare, let wisdom enter your heart and knowledge become pleasant to your soul. Then discretion will preserve you and understanding will keep you, so that you will find favor and good understanding in the sight of God and man. Diligence is like a wise son who gathers in summer; it brings a harvest. So continue to do the good that is in your power to do, and do not shrink back from the effort. The Lord honors the one who does not withhold good when it is due.
Yet, do not let the pressure rob you of peace. A merry heart does good like medicine, but a troubled spirit dries the bones. God is not glorified by your anxiety. He would rather you do your best from a place of trust than achieve a perfect score out of frantic strain. The preparations of the heart belong to you, but the answer of the tongue, and the outcome of your exams, is from the Lord. Prepare thoroughly, then rest in His hands. Even if you stumble, He is like a Father teaching a child to walk, ready to say, “That was a good try. Let’s look at where you made your mistake and go again.”
Finally, know that a good name and a heart that fears the Lord are of far greater worth than any grade. Do not search for your own glory through marks; instead, seek to honor Him with your diligence and integrity. He sees your motive, and He rewards those who trust in Him. I am asking the Lord to give you clarity of thought, calmness of spirit, and the wisdom to recall what you have learned. May you find that His favor rests upon you, not as a bribe for performance, but as a Father’s good pleasure for a child who looks to Him.